I doubt this is a very good idea. If the main creators do not want to share the map, why would they allow you to publish their map again with your name on it? It's kind of sad sometimes that mapmakers tends to stall in the development at some point in time, even with new ideas and interested people.
I'm currently in that situation where the 1st place rock the cabinet winner of 2014 Star Party is hanging forever. I'm pretty much the only one out of four mapmakers that truly wants it to continue. Another guy could help me if I push him a bit but he won't get working back on the map by himself. As of me, I lack time and I have other project with higher priority like helping out DrSuperEvil with setting up the wiki. The map used to be awesome and played alot, even been in top 10 back in the days, now it's a buggy map barely some people remember. But man, is it awesome and internally we have an updated version (that still need polishing) with new minigames and stuff that are probably the best minigame in the whole map.
So... this is it, in your case, if they don't want to, maybe you should respect that. If someone came up to me saying they want to continue StarParty, I'd be open for discussions, but would definitly be carefull with who I share the map.