torx size will be t70 but the ribe sockets are slightly different. not a problem on the smaller sizes but on the bigger ones you may cause some damage to the tool or bolt. it should be a m12 or m13 ribe socket.
definately got mine from halfords when i did my head gasket..... definately ribe ones don't think they were more than 15quid (about 12ish) but cant really remember as it was ages ago but it was a full set... think it was m13 i needed but cant really be sure do know i got alot of other sizes to the one neeeded... as it was the same bit but smaller needed when i took the back seats out of my old car for the seatbelt mounts...
but yea reckon it'd be worth just gettin some new cos they aint much to get and they do come in handy.... if you live near the midlands then you could always just borrow mine but it's up to you