Surely a local TV/HiFi repair shop could manage this? Perhaps Ive been fortunate in my area.
I dont know if they are 'special' sizes for technics (ie the length of the electrical component) but they are usually regular 'off the shelf' "Linear Potentiometers" which in theory anyone with any
qualified electrical nouse could replace.
You shouldnt be paying over 6quid for 'parts' in my opinion.
RS Electronics Catalog (kind of renouned in engineering/trade circles) sell them at about 4 quid each.....so I roughly allow 1.5 hours for labour and 6 quid for the part (maybe a few quid more for a pukka 'technics' model)!!!
If the guy turns round as says thats gonna be £80 - £20 for the part, three hours to fit it blah di blah, he talketh out his arse, lol.
The trick is matching the prongs and the length to fit the PCB, and fair enough, the technics may be an obscure size, but if they are roughly 4 quid to make and sell, dont be conned into like 5 times that, lol
I have found if know what youre on about when saying what the fault is, they dont try and do you (as much)

. Okay the guy needs to make a living, give him a bit of slack, hahah.
Im assuming it is the slider, and not the round one you turn with a screwdriver. The round one should be even less.
See ya
Sirius