You can get them through the CMP 
Look at the Sakos, ... damn can't think of others.
But on the forum that you listed, they have a rimfire side of things. Spend some time reading through there.
The 40x is a nice rifle, but good lucking finding parts for them. Through the CMP you can get a barreled reciever. You need to find the bolt, and a trigger. The trigger is easy as you can use any M700 trigger, but the bolt is a pain in the butt to find.
Look at the Sakos, ... damn can't think of others.
But on the forum that you listed, they have a rimfire side of things. Spend some time reading through there.
The 40x is a nice rifle, but good lucking finding parts for them. Through the CMP you can get a barreled reciever. You need to find the bolt, and a trigger. The trigger is easy as you can use any M700 trigger, but the bolt is a pain in the butt to find.