Allies? Don't you mean mortal enemies?
He'd have a lot of those too, but no, that's not what I was getting at. Let's assume that Khan and his followers would seek out other genetically engineered species to build an empire - a genetically superior one.
The potential for allies is apparent when you consider that Khan believes anybody who is not genetically enhanced, to be inferior to him, and that he and his followers could never live alongside "genetically inferior" species. Of course, building an empire requires numbers, something of which Khan's group doesn't have. The Genesis technology could be used to recruit allies and other followers, on the basis that they hold a weapon of incredibly destructive power.
Khan probably aspired to re-conquer Earth at some point following his escape from Ceti Alpha V - certain that he'd defeat Kirk effortlessly. There are plenty of races that hate the Federation, and since Khan plans to conquer the heart of the Federation, it's sure to attract allies. It's like when the Romulan Empire and the Klingon Empire allied, in a fashion of sorts, because both resented the Federation and hoped to conquer them.