Yes, the receiver channel has to match, but changing receiver crstals is legal and will not cause problems. Keep in mind, if buying a Futaba receiver it will have to be a "Low Band" receiver. Low band is any channel up to 35, high band is 35 to 60. (This is only true for Futaba. )

You can also use Hitec, FMA, or a Tower. Pretty much any "off brand" receiver will work as long as they say "Futaba compatable", which means they're "negative shift". JR and Airtronics will not work (they're positive shift.)

For example, you could buy a Hitec negative shift receiver at an auction, and then get a crystal from the local hobby shop or Tower on your channel. Again, if you buy Futaba, just make sure it is in the low band range.
Dennis-