Nice find - that's got the rare euro powerfeed body, and not generally available on the RT Mag. Check all the seals as these may have perished if it's be sat unused for years. Mags like plenty of oil and often that's as much as it takes to get them working. Make sure you have a full air bottle at 800 psi, as the RT valve won't cycle on low/med pressure bottles. To get the RT (reactive) trigger to function well you need 900 psi plus.
Seal kits can be shipped over from the states and also found on ebay
http://www.ebay.co.uk/itm/AUTO-MAG-AEG-SPARE-PARTS-O-RING-SPRING-KIT-NEW-/181208452149?pt=UK_Sporting_Goods_Paintballing&hash=item2a30dd8c35
http://www.ebay.co.uk/itm/AUTO-MAG-68-AIR-GUN-DESIGNS-PARTS-ALL-NEW-/380521878423?pt=UK_Sporting_Goods_Paintballing&var=&hash=item5898df1397
For some reason the seller doesn't sell the RT/X valve spares kit which is a shame, which as you say means shipping them from the U.S. Doh!