You can still buy MKII magazines. However, I was unable to buy a Volquartsen extended magazine release, and Volquartsen said they had discontinued MKII parts two years ago due to lack of sales. Majestic still sells magazines
https://majesticarms.com/product-category/magazines/
extended magazine release
https://majesticarms.com/product/extended-magazine-releases-for-mark-i-mark-ii-mark-iii-and-22-45/
Clark Custom Guns told me Ruger has dropped their MKII parts. So you have to find aftermarket parts for sears, etc.
A 1999 pistol should be drilled and tapped for an optical sight base. If it is not, call Ruger and see if they will still drill and tap the thing.
https://majesticarms.com/product-category/magazines/
extended magazine release
https://majesticarms.com/product/extended-magazine-releases-for-mark-i-mark-ii-mark-iii-and-22-45/
Clark Custom Guns told me Ruger has dropped their MKII parts. So you have to find aftermarket parts for sears, etc.
A 1999 pistol should be drilled and tapped for an optical sight base. If it is not, call Ruger and see if they will still drill and tap the thing.