This is just a whim at the moment, jury's out on whether or not I want to do it. Have the old VAG alarm you see below, looks like an 80's / 90's Moss one that they've just rebranded. There's no reason why it wouldn't work, but that's immaterial as if it gets fitted it'll be purely for show and not wired up. Have seen this in MK2 images which appear to show a 'L' shaped bracket that runs from the bulkhead, passed the expansion tank, then across to behind the washer bottle. Going to guess it was maybe a proper thing supplied by VW (or VAG UK) as I've noticed it on several different cars now. Yes, I could probably make one but as I say this is just for show so would only consider doing it if it were the genuine article. Hard to see in the images but very possible it's just screwed in at either end which would potentially put me off, if you have one it'd be good to know if yours uses existing holes / fixings instead or not. So... if you have one and want rid of it I may take it off your hands, but not that commited to the idea that I'd spend alot on it, obviously cover postage etc. into the bargain. The engine bay images have been filched off the inter-web, credit to their respective owners!
Interestingly I've just bought a MK2 that came with a selection of NOS alarm bits, no bracket so can't help you there but got a large siren and another slightly smaller siren and ultrasonics branded scorpion for VW as it goes. Wondering if this is worth anything to anyone?