Yippert-
Numrich (e-gun parts) sells barrels for the 39-A, and they do ship to Canada.
Loading gate .22's- there was one- the first Marlin lever .22's used a loading gate, the 1892, IIRC. The 1873 Winchester also used a gate, and was offered for a brief time in .22 cal...
As to the original post- I have a '54 Marlin 39-A that is VERY accurate and smooth operating. No problems with it yet. Also have a 94-22-M in WMR that is quite accurate. Had to replace the fore-end on it though- it started getting loose. Both the Winchester and Marlin lever .22's are reliable and accurate. The 39-A gets my nod over the 94-22 simply because it fits me better...
Regards,
Doc Sharptail