The Preco nozzle and others like it use a toothed belt. While I don’t know what modern-day belt would work, I’d willingly bet that if you take the nozzle and the remnants of the broken belt to the nearest vac shop, they could certainly fit a belt to it.
It looks like a Kirby transmission belt. I imagine a power nozzle with brush rolls on the side might be canidates but Kirby g series transmission belt is my guess.
Les