Some people look for something cheap (any brand) and long enough, or a bit longer, locally (like a used one on FB, craigslist, offerup, letgo, whatever, & then use a grinder (or something) to create a groove in the shaft at the appropriate spots. Bonus is you often get a spare motor.
If you do that, you might be lucky enough to stumble across a cheap one (used or or new) (and likely non-Weber) that still has a box says it has SS shaft & forks.
I didn't need one, but bought one because it was stainless & had a thicker heavy duty octagonal shaft that was machined to a square where it goes into the motor. Was able to see the length on the box & instead of using a grove, it had one of those round clamp sort of things you can put anywhere on the shaft that serves the same purpose as a groove.