What would you use for a new roof install? (composite roof with 3/12-5/12 slope)
For the job that is prompting me to ask, the shingles will be getting removed and new roof installed.
I'm assuming 'shingle' just means typical asphalt composition shingle...
First, I'd try to talk the other parties out of it. I'd say
"Let me treat this just like any job where the roof is not being redone, and I'll come in after the new roof is all done and use my standard flashings. Yes, I'll still warranty my penetrations just like any other job. Otherwise it costs me more in materials and labor and I have to consider whether to charge you for that. The method I'll use is not more likely to leak than the alternative." Also, if the request is coming from the homeowner, then also ask:
"Have you asked your roofer if they are going to charge more for the labor to roof around the solar standoffs?"
If the request is coming from the roofer, who insists their entire warranty is voided if you make one hole after they are gone, then here's the answer to your question...
The only complete product I'm aware of for this application is Quickmount PV Qbase composition mount. It's expensive but it avoids any question of whether you're using something completely engineered for the purpose, and it comes with all necessary parts. It's what I've used lately in these situations.
http://www.quickmountpv.com/products/qbase-comp-mount.html
Alternatively, for less money, you could use ProSolar Fast Jacks or Unirac 4" standoffs and buy the properly sized Oatey flashings with built-in collars. You know, the really old school method.