Amazon has them for $1325. They command premium prices in certain circles. As an aside, I think the Denon 103 MC cartridge is a good match for that arm. Enjoy.
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Consider the missing headshell a good thing and don't scrimp on the replacement. Get one (or more) of these. The ZuPreme headshell is a more solid mount, adds some effective mass to the tonearm for a wider variety of cartridges, has higher quality lead wires, and has adjustable azimuth. I consider this headshell to be the first step in getting better performance from the SL12x0 series.
I've been using the Audio Technica AT150MLX on my SL1210M5G for 4-1/2 years now. It is a great match. In my case, it could turn bright if the cartridge wasn't seeing a 100-200 (preferably 150) pF capacitive load. It also helps to wrap the tonearm in inexpensive Teflon pipe thread tape. This quells an upper midrange resonance where the tonearm tube rings. After taking care of those two things, my AT150MLX is lush with detail, linear, full-bodied, with extended bass and realistically (but not exaggerated) airy treble.