Do not atttempt this. Find a gunsmith.
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.
Download a manual from Browning or take it to a gunsmith
The browning web site will provide this info.
BAR stands for Browning Automatic Rifle, not browning association rifle.
Let a gunsmith do it.
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.
Leave this to a qualified gunsmith, trust me on this.