I've been investigating windscreens, a deal-breaker for my intended use of the micros. I already have the AT853rx mics which work great for sbd+aud matrixes with my UA-5. I am not so sure they would be festival-worthy, so I'm looking to upgrade.
Anyway, the diameter of the AT853 is about 1/2", or 13mm, slightly larger than the micros' 10 mm. The standard windscreen, the AT8102, stretches to fit snugly, and might be a good all-purpose screen for the Audix M1290. I have not had my ATs long enough to do any outdoor taping, so I don't know how well the AT8102 reduces wind rumble.
There are two other windscreens designed for the AT853; the AT8117, and the AT8104A. The AT8117 is a large, high-density foam windscreen intended for outdoor use. Never having used it, I can't vouch that it works as intended.
The AT8104A is a 2-stage, lockable, metal windscreen with foam outer screen. Looks heavy-duty, but again, no first-hand knowledge of its performance.
The cost of the AT8102 is about $8, the AT8117 about $10, and the AT8104A is $48, from a known vendor. Just throwing this out there for you Audix micro owners. If you're not stealthing with them, maybe a good windscreen would make them suitable for taping at festivals, and the like.
P.S. Nick, if your vendor won't make good on the screens, maybe you could try out the 8117 and see how they work. If they don't fit, I'll take them off your hands for my ATs. E-mail me for vendor info.