In many guises this has been discussed here before. At the end of the day in a situation such as yours you may have to cast a wider net. Look for programmers with wide language experience. For a widely experienced programmer Perl offers some subtle edge cases, but generally DWIM saves the day. From personal experience I can tell you that a good programmer can come to Perl cold and be doing good work in a couple of weeks.

It's generally the problem solving ability that you need to target rather than detail knowledge of a particular subject. If you have time to bring someone up to speed with Perl you could well win over the term of the project by looking outside the immediate Perl community. When you do, introduce them here and their learning time will be cut to 1/3 :).