How can I buy a VHF wireless mic separately?

[Jorabi]

I have a VHF wireless system that came with two handhelds and I need one handheld and one lapel. The company does not make a lapel. Is there any way to buy a different brand mic separately that has a customizable frequency (either by me or at the factory)?

 

[Alabalcho]

If you mention make and model of existing equipment, someone can jump in with recommendation. Everything else would be a wild guess.