Never came across the Telefunken ones (didn't even know they made anything except mics - and, according to the jolly lads who set up Zappa's PA system, marital aids....)
When I worked for (oh, the shame of it!) Guitar Center in '83-'84 I fell in love with Modulus picks; thinner than a Fender medium, stiffer than a purple Tortex. Last thing I did upon being given the boot was (they, woe is me, having just been discontinued) grab a dozen - which were, alas, scattered by my children decades ago.
A few years back (OK, maybe more than a few.....) I was able to procure 6 Adamas ones from a club member (Edwin, maybe?). They're 2mm, which is thicker than the Modulus ones I loved - but still better than any production plectrum I've tried. I don't let my kids (now middle-aged men) anywhere near them - not even the one picker in the lot!
And I did specify "production"; my 2 favs (and I think I may have had you try these ones, Bill) are a glass pick given me by the eldest, and from the youngest, one carved from 50,000-y-o fossilized walrus ivory.
Let us know if you find either a source or a substitute; even fingerpickers need a new flatpick every now and again.
Peter
Peter