Last week at the Ace I was asked about steering rack boots....so I thought I'd post what I have found for reference.
The GTA and A610 use commonly available parts.
For the A610- power rack, the boots are 7700706007- also found on r11,18,19,20,21,25, Mk1 Clio Espace Mk1 and Mk11- all versions with power steering. I got a pair for under £10 at my local factor and they were on the shelf there.
For the GTA the boots are handed and for manual rack versions of the cars listed. 7700680852 (RHS) and 7700653459 (LHS) and they come from R25 diesel, R30, Trafic (and the Fuego & Spider too) all with manual steering. I haven't tried getting any but I'd try your local factor for those too.
I hope that this helps someone!
Cheers
Lee