ContactTower
Co-incidently, I did (or rather tried to do - was screwed by crap weather) a glider course at Lasham a month back, as a qualified (140+hr) PPL they were keen to point out (dropping large hints) they were short of tug pilots. Apparantly there was a waiting list but isn't one now and were trying to get me interested. So they may be worth a try if you are keen. They have a couple of nice Robins, a very smart Cub 180 (which I would love to fly) and a Pawnee.
Look at their website and navigate to the Tug pilots notes/training (something like that) to have a look at their training requirements, they are quite extensive and will require money from you to do it. So it's not just a matter of flashing the old PPL and logbook and having a couple of check flights.
Bear in mind, tugging is not for the faint-hearted and from what I've seen, can be very hard work (esp. on competition days) requiring some degree of stamina, commitment and dedication to the cause (of gliding). Also, consider that the flying is very much: take-off, up to 2000', drop, land, repeat, for some people - myself included - this is not what we fly for and personally, I would get very bored very quickly, hence I'm not interested but if you are, give Lasham Gliding Society a call, it may be right up your street.
Whatever you choose, I wish you well. Good Luck.
As an aside, I've been told quite a few glider clubs prefer not to use CPL/wannabe CPL's as they tend to be enthusiastic right up to the point they get the call from FlyRyanEasyThompsonJetBe whereupon they vanish overnight leaving the club sans Tugger. However, check locally, every club has it's own rules/bias/preferences. This also includes how much glider experience is wanted, some want Silver level some just want 'Some experience' - unspecifed.