I am trying to assemble a bike for someone in my family. There are a few challenges. The first is my limited experience, the second is her wish-list, which includes using a 27.5" MTB frameset she already has, a limited budget, and a preference to not use a MTB-style suspension fork but a lighter-weight rigid fork.
The headtube expects a threadless tapered steerer, 1-1/2" to 1-1/8". With the limited budget, that leaves only a few choices: low-end all-carbon or an alloy steerer with carbon-blades. I have seen many low-end carbon forks on eBay, Amazon, and Alibaba, but the reviews are sprinkled with comments like "I had to take a dremel to the dropouts". So I would really prefer to get one with an alloy steerer from a "brand name" bike manufacturer. But they all seem to be straight 1-1/8" steerers, not tapered.
Is there such a thing as an adapter for a headset, whose bottom bearing assembly is a 1-1/2" to 1-1/8" adapter, something along the lines of this mockup: