This is best left to a factory trained gunsmith.
Try want ads, for sale ads, gun shops, gun shows, estate sales, garage sales, pawn shops, egunparts.
HIghly recommend you leave this to a trained gunmsith.
First, get a copy of the owner's manual. If it was made by Browning, go to Browning.com and request one. Second, follow the instructions.
If you are not trained to do this, I recommend you do not try it. Chances are better than even you will be taking a box of parts in to a gunsmith and that's not good.
The browning web site will provide this info.
Download a manual from Browning or take it to a gunsmith
Let a gunsmith do it.
BAR stands for Browning Automatic Rifle, not browning association rifle.
Correct terminology is 'inner magazine tube assembly.' The BAR22 and BPR22 used the same part, we occasionally have them for around $23.
You can request a manual from the company.
Best bet is to ask a gunsmith for help.