Any authorised VW dealer i would presume. Just tell em its for an anniversary golf or an early vr6
The anniversary gti's all had the deeper ones, mine came with a smaller one i think because it prob got caught on a kerb and disappeared at some point b4 i bought it and they replaced it with a shallow one (fools)
They've had my exhaust replaced too and fitted a normal gti back box instead of the anni chrome one