The TL3 is a p-mount pickering branded version of the XV15 and 680 family.
Stereohedron was pickerings variation of the Shibata style line contact stylus, so that means it has a smaller side radius - so it tracks high frequencies better, and a larger major radius, so it has a long contact patch, which results in lower wear and tear on both the stylus and the records.
Stereohedron = Shibata = LineContact
Other Line Contact types include VividLine, Fineline, HyperEliptical, Hyperbolic, etc...
There is a notch up on this type of needle which is the Van DenHull, Fritz Geiger, MicroLine, MicroRidge type.
The TL3 was available in a basic model with DLT3 stylus and a stereohedron model with DTL3S stylus - which made it a TL3S
Here are some Pickering specifications:
http://www.pickeringuk.com/spex.html
The model down from it TL2S, and up from it TL4S are still available new at:
http://www.pickeringuk.com/T4P.html
You can get the original DTL3S here:
http://www.turntableneedles.com/DTL-3S-Needle-609-DEX-Genuine-Pickering_p_731.html
or you can fit the DTL2S or DTL4S:
http://www.pickeringuk.com/styli.html#T4P
Or you can get one of these which will also fit:
Basic Eliptical
http://www.lpgear.com/product/PICSDTL1E.html
Better Eliptical
http://www.lpgear.com/product/PICSDTL2E.html
http://www.turntableneedles.com/DTL-1E-Pickering-copy-Needle-609-DE-tall_p_1067.html
Best Eliptical
http://www.turntableneedles.com/DTL-2E-Needle-609-DEL-Genuine-Pickering_p_1212.html
Stereohedron / Line Contact options
http://www.turntableneedles.com/DTL-2S-Needle-609-DEL-Genuine-Pickering_p_1213.html
http://www.turntableneedles.com/DTL-3S-Needle-609-DEX-Genuine-Pickering_p_731.html
http://www.turntableneedles.com/DTL-4S-Needle-609-DEZ-Genuine-Pickering_p_732.html
Note: if the arm you are fitting it on has adjustable VTF you can also fit the styli with brushes for the Pickering XV15 / Stanton 680
Eliptical
http://www.lpgear.com/product/STAD6800EE.html
Line contact
http://www.lpgear.com/product/STAD6800EEE.html
http://www.lpgear.com/product/STNS680EES.html
If you want to know what it can sound like - do a search on the Stanton 680 - there have been a series of threads on this cartridge... and it is excellent.
The Lpgear vividline or hypereliptical styli (the last two line contact links) - are highly recomended as being excellent value for money... the original OEM stylus at around twice the price may be better (maybe)
bye for now
David