Hi Lambros,
I don't have a part number, there really wasn't one, they came from AutoZone, a local chain of auto parts and accessory stores similar to PepBoys and the like. They are metallic blue in color and made by Gabriel and were the only shocks that AutoZone carried for the VW Beetle application. They cost around $20.00 for the pair and are great!
Someone mentioned that JC Whitney (of ALL people) has a similar shock for sale supposedly made especially for them. I bet that Gabriel is offering one of their low end (softer) road shocks to various outlets and that the ones at PepBoys or O'Brien's or AutoZone or whomever are all the same item.
Try a local generic auto accessory store, just make sure that you ask for Gabriel and I bet that it's the little metallic blue one.
If you have no luck, let me know and I'll hit AutoZone for you and see if they're still selling 'em, probably grab an extra pair for myself while I'm there.
Luck,
TC