Random Draw Question

I need help with a random draw formula. Here is the situation

There are 8 teams with 5 squads each for a total of 40 squads. Each squad is numbered 1 thru 40. Each month a random draw is held to match two squads to compete against each other. However, you do not want anyone on squads 1 - 5 competing against anyone else from squads 1-5. IE: team mates, and you would never want two squads to duplicate any of the previous matches in following months. This draw would occur once a month for at least 6 months.

1 =RAND() =RANK(B1,$B$1:$B$40)
this formula works for random draws, but it does not exclude team mate against team mate and could duplicate a pairing in following months.

suggestions???
Thanks
Chad Kellner

I would suggest a macro approach to this one where you store a list of the previous pairings and get the macro to loop generating random matches and rejecting those which either are already in the list or are between two squads in the same team.

This is not fool proof as you might get a situation in which the only two squads remaining are eiher in the list or team mates. In this situation you would just keep rerunning the macro (or even get the macro to re-run itself) until you get a satisfactory outcome.