There have been a couple post from purchasers on rimfirecentral.com. The bolt appears to be the same as used on Nordic Component dedicated 22 LR uppers. I suspect these are Wilson air gauged barrels from Wilson Arms in Connecticut, not Wilson Combat in Arkansas. With Compass Lake Engineering (CLE) not offering their dedicated service rifle trainer RRA is about the only option. Bore Buddy is selling a 20” rimfire upper but uses a different hand guard. The 20” barrel can be purchased and you can use a CMMG Stainless bolt.
If you want a fully functional bolt catch the Bore Buddy barrel and CMMG bolt is what I would assemble. PSA has the CMMG bolts for $99.99 and the A-2 hand guard and free float tube can still be found.
RRA still sell the free float DCM pattern barrel sleeve and you can buy an A-2 Fixed sight tower that his held in place by four allen screws instead of having the front sight pinned.
https://www.rockriverarms.com/index.cfm?fuseaction=category.display&category_ID=1263
DEZ Tactical Arms sell the A-2 front sight held on with set screws. I used one of these on a 22 LR AR-15 build about 15 years ago. I used red Loctite and his has held all these years.
http://shop.deztacticalarms.com/products/dez-tactical-arms-dez-1034-gb-751778882946-dez-1034-gb-6422
Here is a link to the complete A-2 sight including the post, spring, detent.
http://shop.deztacticalarms.com/products/dez-tactical-arms-dez-1035-gb-751778882922-dez-1035-gb-6422
Bore Body Match Barrel
https://borebuddy.com/product/borebuddy-apogee-match/
Palmetto State Armory 22 LR CMMG Bolt with barrel collar.
https://palmettostatearmory.com/psa-22-lr-bolt-carrier-group-stainless-steel.html