Do you know if these parts are attracting the attention of reproduction part manufacturers? it kind of seems that some parts are reproduced like some firing pins, safety knobs, and dust covers. It also appears that this rifle has a small "cult" following for people who enjoy shooting these rifles. Am I correct in these assessments?
Some of these parts are easier to reproduce and have larger markets than others. Mauser firing pins, because of the huge number of mausers, are one example of new production firing pins. 1903 barrel bands and trigger guards are another area and probably Mauser trigger guards in the new future. Triggers and sears could probably be reproduced but not at the prices that folks would pay as they would be close in price to aftermarket triggers such as Timney etc. but still be inferior to such.
Idiosyncratic parts such as dust covers that are easy to make from sheet steel, slings, bayonets for some reason, cleaning rods, etc. were often discarded or worn beyond repair by original users and represent a significant part of the repro market. Reproduction barrels are another common part.
Stocks are another area where a fair number of reproductions exist for certain rifles but the demand fluctuates based on any new/used influx of original stocks, the availability of modified rifles in the first place, and how easily the original stocks can be restored. Ironically, repro handguards are often scarce and some of these, such as for the different models of Krags which used different sights, run nearly $100 for repro models. Things like original T38 or T44 carbine handguards or even run of the mill T99/T38 handguards are often difficult to find and pricey when you do. These are also parts that often crack, were damaged by sporterizing, etc. which is why the demand exists in the first place.
For liability reasons and costs of production, the least common reproduction parts are receivers and bolts followed by things like barrel bands, odd screws for things like iron sights or barrel bands, barrel band springs, issued iron sights, buttplates,and so on. When you get into things like semi auto receivers of full autos, there are some but these have often gotten bad reps for being out of spec and the cost for bolt action receivers led to investment casting rather than forging like the originals and some of these are even dangerous (see National Ordnance 1903 receivers for example) or wear quickly--see some commercial M1 carbine receivers for example.
Until rather recently, Arisakas were plentiful and mainly treated by many as junk due to blowups--often because of bad rechamberings to things like .30-06 or using things like the cast iron training rifles or worn school rifles. They really did not begin to climb in collectors' esteem until the 2000's for the general run of the mill rifle. Thus, relatively few replacement parts have been made--
Btw, if you do get an aftermarket replacement firing pin, it will have to be fitted to the rifle or otherwise you risk either light strikes or pierced primers if the firing pin protrusion is greater or lesser than the required range or the end of the firing pin is not in the proper ball headed shape. I bought one to fix up an old Arisaka with a worn safety and firing pin (chipped release surface on it). The firing pin tip was square rather than rounded and I had to shape it to a rounded shape. I suspect part of the shortage of Arisaka firing pins and safety knobs is either through Bubba trying to do a trigger job and buggering up the firing pin release surfaces (aka cocking surface on the firing pin) and through natural wear as the safety surfaces inside the knob can wear and allow the rifle to fire if dropped or simply not apply in the first place.
Due to the hollow nature of the Japanese firing pin which is rather unique apart from the MAS 36 type, these are not the simple lathe job of producing like the solid Mauser type firing pin (or most of the other Euro designs like the Enfield, Mannlichers, Mosins, or even earlier French rifles like the Lebel or Berthier ). I also suspect that the vast stores of replacements for these rifles also did not exist for the Japanese Arisakas as few countries used them and Japan probably destroyed and recycled a lot of the spare parts as scrap after WWII. Thus, most Arisaka parts are from disassembled rifles by individuals or from discards from gunsmiths sporterizing rifles.