I may be wrong, but I think that the Thorens original is the only one that is correct. I have seen quite a few photos of the arm with other Thorens headshells fitted and they are clearly not correct, with the offset angle to the main armtube being all wrong.
I am surprised that you can't find one for sale, but be aware that when you do, it may be quite pricey.
Did you try searching German and Swiss sources?

So I can't use a proprietary sme headshell of the same weight on this arm. I know they make 2 headshells the TP50 & 60 which fit specific arms. I was hoping that the straight TP13 arm could take a variety of other headshells but appears not

The shell is specific to this era of tonearms - the TP16 arm has a straight pipe and offset headshell, although I think the plug and socket are related.

Don't despair and look around with patience as they do come up fairly regularly, or at least they used to. The TP13A isn't the last word in low friction, but it can be serviced and kept stable and sonically I don't believe it to be intrusive. Most modern cartridges track securely at 1.7 to 2g and the likes of a modern AT would be fine for it I think (I think the Goldring E3 screws in from the top sadly). The screws are a fine metric thread (2mm?) so you'll need to make sure you have some of these as well.

Main thing with these decks is to ensure the main bearing spindle isn't wobbling in its sleeves - some later ones do (TD125mk2 and early TD160's) but the 125mk1 and possibly all 150's don't. I used to recommend EP80 viscous gear oil, but was hauled over the coals as some or all Hypoid oils may have additives in them not compatible with sintered bearing sleeves. Current recommendation for main bearing oils is Stihl chainsaw oil once the old stuff is cleaned out, as it's apparently sinter-safe? and has the right kind of viscosity in various turntable bearings. Thorens used a light turbine oil in their turntables, but I don't think it's available in anything less than a massive drum now and if there's a small amount of wobble, a viscous type will help fill the gap a little and with beneficial sonics to boot.. I have no idea what oil Thorens use now, but a call to their distributor may be very helpful to you and I perhaps.. Sorry to mention this aspect, but if the deck is wanting here, then nothing else you do to it will fix a very music-destroying problem in my opinion and experience.

Brilliant thank you, I'm really interested in this TT and would appreciate any help with this

This is my current headshell

Google image search on the arm model no. will show you the pins are longer and I seem to remember the diameter of the part they emerge from is different to the SME pattern too.

Hi I have checked and as others have already indicated the Thorens hesdshell is not compatible with the SME type.

Hi again, were you specifically wanting to use the original tonearm? I have used both a Logic Datum a late issue MK1 and a Grace G707II tonearm with a MK1 TD150. Both combinations work very well. The Grace/Thorens combination is in regular use by another member of my family and sounds fabulous. The Thorens arm board can be changed quite easily if you are happy to disconnect the arm lift cable and the output cables.

I ended up dodging a bullet tanks to the hell from you lot. The turntable had no lid or headshell and after pricing up the pair it looked a very expensive deal.