Vacuum switch

[mewethington@domain.elided]

     HELP!!
     
     Woe is me....I just discovered that my vacuum advance switch is broken 
     and I need another.  I think that the proper name is a "ported vacuum 
     switch."  It has three connections (nipples) and it runs off of the 
     distributor, (I think)  I believe that it is some thing for the 
     emissions, mine being a '79 Scout II.  I called International trucks, 
     but they want $93.00 for it....yeah right.  It's so expensive because 
     it has a thermal switch in it that either allows the vacuum to flow or 
     cuts it off once the air is hot.  (I'm a little ignorant to it because 
     I'm at work and my dad is relaying me the information over the phone.)
     
     I'm going four-wheeling this weekend and would really like the engine 
     not to die off the line, therefore I need it ASAP!!!
     
     Any suggestions or possible "bolt-on" replacements??
     
     Thanks guys.
     
     -Mike Wethington
     "In desperation of three nipples"