Did you build your 2641's from a kit? If you did, then you are probably aware of this:
http://acoustic-visions.com/~acoustic/products/speakers/complete_kits/pdf/kit2641instructions.pdfI would think you could still get the Usher 9950 tweeters.
As far as the midrange and woofer drivers, I would guess you could probably try to find matching drivers with as close of TS parameters as the original Adire drivers.
Or try to find the Adire midrange and woofers, if they are still floating around.
The pdf shows dimensions, part list, and everything else.
I've had a pair of Usher 9950 tweeters for a few years.......they are a good tweeter.....boogie right up there next to Scanspeak.
I was playing with a pair of ESS model 10 bookshelf speakers the other day.
The original tweeters are too bright for my taste. Using a tube amp helps, but it's still objectionable to my ears.
I recalled my Usher tweeters...hmmm...they dropped right in......
The original tweeters are more sensitive than the Usher 9950's, but things sure did smooth out soundwise.
I swapped out a 5uF non-polarized electrolytic for a 6 uF polypropelene, and they sound rather good.
For a bookshelf speaker.......rather strong bass for a bookshelf speaker as well.