I thought the mk2 didn't work with any other locator boxes or collars? They made the mk3 because they realised they had dropped a bollock with the mk2 because it was completely crap, they rushed it out and hadn't field tested it enough then when they realised where they had gone wrong the mk3 came out very soon after and I think they discontinued the mk2?
your right got a mk2 box had collar lossed it couldt get another mk2 only works a mk2