Edit: Here’s a more up-to-date Crew Creator built by Ratty from the Wyrd forums. Thanks to Michael (see below) for the link.
Malifaux crews are pretty easy to put together as there are so few models in each game. That said, I stumbled upon this handy online Crew Builder. I’ve only given it a limited test, but it seems to work well. It allows you to add models up to a soul stone limit and it automatically calculates the unused soul stones for your master’s total.