Texas Pooh is correct. This is where the rubber meets the road.
But, in your state, substituted service is acceptable, and you can make service in Small Claims using certified mail, the Sheriff/Marshal or a registered process server. None of these work? (They're not evading; they're hiding.) A process server can do a stakeout if it's worth the money.
Your problem is only "Part A". If they are that hard to serve, have you worked out a sure plan for enforcement? That's "Part B", and it's going to harder.