Would your husband be comfortable if they were friends, or if you went on dates while he was gone, not just had sex partners?
If dating is OK, I'd try OKcupid.com if (polymatchmaker.com too if you are in a larger city) So many poly people are SO busy with relationships, I don't think it would be that impossible to find somebody who you enjoyed spending time with and had chemistry with who ALSO was willing to see you on your husband's travel schedule without it making them feel like a cheap sex toy or something
It might be preferable for a lot of people who don't necessarily have time for a relationship where they need to have time available weekly.
Of course whether you date or not, there is the chance that you fall in love with somebody else too, and that is something you two husband should really accept as a possible consequence, no matter how casual your relationships are planned to be.
edit: Just wanted to throw in, I think STI wise, it can be much smarter to choose longer term FWB or lovers than strangers who are just there for sex. With all the strains of both low and high risk HPV around that condoms don't protect from, with the high rate of HSV-2 (if that is concern to you) having a better idea just who you are getting involved with can be a bit more important to be aware of when there are other partners health to consider.