I've had the same oversize problem, I actually had to grind a couple of my 16C collets to fit the material we are getting, ~1.505 and ~1.230. We did get some precision aluminum stock in one order that was on size, but if you ordered that as precision stock I suspect it would be expensive. The last batch of 1 1/4 that we got measured at around 1.249. We buy from a large vendor, but we are buying by price rather than precision.
Hardinge will make collets in any size you want....... for a price $$$$ They might stock some over size collets.
Using emergency collets might be the best option.