I suspect the nearest approximation could come from from a RLH door of a 5dr hatch; so far I've only been able to locate a reg from a 306 cabriolet; not sure that would be right shape or size.
I don't know the first thing about these cars but if you're having a hard time finding replacements, repair might be the best option.
Based on what I have seen on many other cars, the mechanism itself is a mirror image left to right so a few rivets could be extracted and the whole mechanism assembled back in a mirror image configuration. Motor/g'box casings are sometimes handed, but the innards are not, so your old casing is still useful. Front to back (same side window) I don't think the motors would be any different. Might have extra holes/studs/bosses cast for mounting.
IMO Don't bother with repairing the cable and the plastic wheel. If the cable as broken you'll probably find it's chewed the wheel. Getting the cable length spot on (a lot of Ebay Kits are wrong), with a end stop crimped hard enough, they are a hex shape and hard to find, then installed under tension, on an existing rail that has brittle plastic bits from years of heat, is just not worth it - I've been there and it's hell. I'm not sure if these guys stock your model, but I got a new reg/rail/motor assembled and it's a straight swap (cables requiring soldering or spade connections if you're lazy) for $150 or something delivered. It was money well spent. (https://www.electriclife.com.au/) No affiliation. If you can source a salvaged one that's also an easy option. Mine was a 306 S16 - a pretty rare car and they had it stocked in AUS which is unheard of for this vehicle.