I've got an old 1981 Ross Gran Tour 10 speed that I've had since it was new and it finally needs the chainrings replaced due to wear. But this bike has a rather strange setup compared to more modern bikes, so I don't know what approach to take... and skip the "get a new bike" advice - I'm keeping it for sentimental reasons.

The bottom bracket on this bike seems to be standard (Hatta brand from what I can make out with the cranks on), square taper axle with bolts that screw in to retain the cranks. Both the cranks and chain rings are aluminum alloy, (Shimano?) Tourney.

Instead of the normal setup with a spider on the crank to hold the large chainring, the chainring (or chainwheel?) seems to ride directly on the axle, being held on by the crank. Looking from the inside, it looks as if there is some type of collar in the center where the chainring meets the axle. Attached to this large chainring is the small chainring on the inside and a chain guard on the outside.

Someone (not seeing the bike) at the lbs mentioned that the setup resembled that on a BMX bike. Having never studied this before, I wouldn't know. Looking at parts catalogs on the net, there appear to be these single chainrings/chainwheels that are either solid or cutout, but with a single hole in the center for the axle. I've also seen collars/adapters of some sort that fit into those holes for the axle to go through. But both the hole in the chainring and the hole through the adapter seem to be round - what keeps the chainring from rotating on the axles?

Is there any possibility of replacing the chainrings in my current setup? I haven't been able to find any such replacement parts on the net; are they available anywhere? I suppose even if BMX uses a similar setup, there would be lots of other differences prohibiting using their parts - different chain, just a single chainring, etc.

I suppose the expedient solution is just to replace the cranks and chainrings totally with new parts. If that is the case, does anyone sell cheap double chainring cranks that would fit? Would a triple work? I have the old style friction shifters, so there are no detents - it's always been shift and adjust so it sounds right (Shimano Altus front derailleur).