Originally Posted by MaysEffect

Gotcha, In any case, no matter the brand, i recommend a hard domed tweeter rated between 15-30 watts rms.

Silk dome or paper/fabric domes will not withstand heat as well (sun point directly down on these) nor have better upper mids attenuation. Also they can't survive distortion as well as hard dome tweeters. Given the fact the speaker placement isn't firing directly towards you, the slightly brighter sound of the hard dome design will not be anywhere near as harsh.

Here is a small list -

MB-quart - ZT1-25 (best quality), DT1-25, XT1-20
Pioneer TS-T110 (recommended)
Rockford Fosgate PRIME R1T-S

I checked with the speaker adapter site, and they do still offer these adapters.