I have a race bike with a SM-BB70 fitted, will a SM-BBR60 fit?

No, the BB70 is a 73mm MTB BB, the BBR60 is a 68mm Road BB, on the basis you have an MTB, you have a crank which uses a 73mm shell, the BBR60 will be 5mm too short.

The BB is on a 2010 Canyon SLX road bike with a Dura Ace 7900 crankset

A SM-BB70 is a Deore level MTB BB https://bike.shimano.com/en-US/produ...o/SM-BB70.html are you sure it's this model?

I got 1 link saying the seller stopped carrying the BB70, so I guess you Must seek something else..

Though Wholesalers to bike shops keep more old parts on hand for repairs , that trend driven online shops don't re-order.

Why is this an issue? Shimano often discontinues parts like BB's when they have a new generation out, so only one SKU is kept, all you need to do, is buy the current SKU (it will do exactly the same job). The BB70 is old, and was one of the first generation HT2 BB's.

General theme in bike repair parts the distributors my LBS uses, have parts long after the latest trend has moved on.

I believe the BB70 was compatible with both 68 and 73 mm bb shells and came with the spacers necessary to allow a 68 mm shell width while using a 73 mm MTB crank spindle. If so, by deleting the spacers it could be used with a road crank and a 68 mm shell. Apparently that's what the OP has

The the BB-R60 should serve as it's replacement but an adapter will be needed to use the bb installation tool for the BB70 as the R60 cups are smaller in OD. A plastic adapter is included in the R60 package.

Thank you HillRider