With Legion growth stalling, Ryan Routh, a former construction worker from Greensboro, N.C., is seeking recruits from among Afghan soldiers who fled the Taliban. Mr. Routh, who spent several months in Ukraine last year, said he planned to move them, in some cases illegally, from Pakistan and Iran to Ukraine. He said dozens had expressed interest.

“We can probably purchase some passports through Pakistan, since it’s such a corrupt country,” he said in an interview from Washington.

It is not clear whether he has succeeded, but one former Afghan soldier said he had been contacted and was interested in fighting if it meant leaving Iran, where he was living illegally.