The first brand you can begin looking into is Dimarzio's since Andy Timmons is listed as a user. Have a look at Seymour Duncans as well. You could narrow your search to the low-to-medium output range on either brand. The clips on the websites may help a bit.
To my ears, Andy's tone has a smooth, clear vocal quality - the kind that PAF equivalent humbuckers can deliver.
So I would work on getting the neck humbucker decided first and then looking at a complementary bridge humbucker.
PAF styled neck humbuckers would be my recommendation for the neck slot. These should give you rythem and singing lead tones. Look for those that clean up well when you back off on the volume knob.
The bridge humbucker could either be the neck's equivalent, or else, looking for something with a tighter bass, preferably not too dark since the Custom 22 has a mahogany body (but you would know best as to how much bass is already being tightened up by the Custom 22's maple cap).
I have a PRS that I fitted Seymour Duncan 59's to. The pickups are very thick sounding - great for rock, the bridge may not be as tight sounding as you want if you need it for metal. SD's website should have some clips for you to listen to.
You could consider an alternative route that Im in the process of deciding on:
- I would like to try handwound humbuckers by some of the small-scale pickup winders. I'm looking at WCR humbuckers for maple cap/mahogany body guitars. PAF tone is elusive because there is no consistent benchmark on what it is - various industry people reckon there are 4-5 ballpark PAF tones - hence you see these manufacturers offer multiple PAF styled lines.
Hope the above information helps.