I went through this recently with mine as the tensioner was in the same shape as yours is presently. No luck on a NOS part anywhere so I kept looking on eBay and found a used one that looked pretty decent and bought it. You can never tell though and when it arrived it was quite good, so it is going into my motor build. I did consider Cappellini, as they have a gear wheel and a replacement shaft that the gear rides on for a solution. It looks like you would have to have the existing shaft area machined out to remove the old part. Then the supplied new shaft has a bolt/screw affair to attach the gear wheel part into your old assembly.
I think the part was around $120US for the basic kit as described above. If you wanted the complete turn key assembly with all the parts it was quite a bit more like $350US. I will try to find the seller and the part again to give you an idea. They are in the LA area, as I bought a few items from them already and good to deal with... just expensive parts.
There are two sizes of the rubber wheel on that tensioner, so two kits are available depending on the rubber wheel/gear size.
Here's the link to Cappellini in italy and their website with Euro prices. I tried to buy direct, as they are way cheaper and phoned them. No cigar!
They use a European distributor and a US distributor and they both upcharge big time based on their website's Euro prices. Those shift forks are 150 Euros which would be about $200.00 Canadian.
The US distributor is $512.00 Canadian with todays exchange rate, plus shipping and Canadian taxes would be well over $600.00. :angry:
I'm in the wrong business it appears.
http://www.cappellinimoto.it/catalog/motorbike/CB72/product
Here's the US based stealer....I mean dealer on eBay.
https://www.ebay.ca/usr/valtermotousa
At least your paying in US currency so that helps a lot.