Are there alternatives to an NHT X1?

We inherited a set of NHT speakers.  We have one A1 amp, but no X-1 crossover.  I cannot find an X-1 for sale online.  Based on the diagrams, we need an X1 and another A-1 to power the subwoofers properly.  Is there a workaround?  FYI - we are novices so please forgive any basic questions:)