We really need to shed some light on this. Even if they have filed a refugee claim and they're working elsewhere, they still have a responsibility under the contract they signed with you. Therefore, if they are working somewhere else and they are declaring that income, then the government can trace them and remind them that they have a contract somewhere else and they have to fulfill that contract first.
Furthermore, you appear to be saying that you want to move on and not carry this case on forever. However, if you were to be able to trace these individuals, you wouldn't be able to receive compensation from them. On the one hand, you can't find them and on the other hand, they probably are not making enough of an income to reimburse you for the amounts in question.