World wide web.....
There are many, many sources now for Glock custom work or after market features.
Go on Facebook or Instagram & you'll see nearly every color, part, barrel, sight, add on & gadget you could think of for a Glock pistol.
I'm a Glock owner now(Glock 21 gen 04 .45acp). I might get a new gen 04 Glock 23 .40 later on too.
I'd check these sites;
www.glockstore.com ,
www.glockworx.com www.robarguns.com www.boatmanbooks.com www.customizeyourglock.com www.brownells.com www.glockmeister.com www.mahovskysmetalife.com www.apwcogan.com .
Many Glock owners & armed professionals like Cerakote. It offers a lot. I heard Bearcoat from Rocky Mountain Arms is top rated too. The hunting/outdoor company Cabela's did a extended T&E of gun treatments and the Bearcoat firearm surface treatment worked best, outlasting many others.
I'd add 3 dot night sights. I like the orange/green style HDs from Trijicon.com . Trijicon is in use with many LE & military units around the globe.
I also like the after market Glock parts from
www.tangodown.com . Larry Vickers, a retired US Army soldier & former SFOD-1 member R&Ded a magazine release & slide release(that is like the M&P style). Both Tangodown Glock parts come in black or FDE tan.
A GTUL comes in handy for cleaning-checking Glock pistol magazines. I got a kit from
www.midwayusa.com with a brush/Glock tool. The GTUL helps quickly & smoothly remove the magazine base pad.
Some Glock owners add a Hogue rubber grip to the frame but many dislike them. Youtube gun channel host & trainer; James Yeager,
hates them. I don't use any right now, but I can see the merits for a casual shooter or CCW holder that prefers the feel-grip. I'm not fond of the Glock RTF texture but my 21's design isn't as bad as the first series of Glock 22's. That was awful IMO. Glock had them way too sharp & rough on the palms.
Some get the after market treatments for Glock frames. Glockstore has a few great offers. I might get the basic package from them or Glockworx.com that includes the rounding of the front trigger guard. I prefer rounded styles but that's minor. I might get a new Glock/Glockworx.com Ti take-down lever. The standard Glock part is to small & awkward to field strip quickly.
The Ti pins & parts are nice but not a mandate for any Glock pistol.
Some gunners like the late Robert Boatman & trainer James Yeager say to keep the guns factory stock as much as possible. I agree with them but the Glocks can benefit from a few upgrades by trained armorers or professionals.