easy as mang, just rock to TOYOTAZ or manawatu commercial and 4x4 wreckers in palmy (keith st, or armstrong street) and get one off a hilux diesel then get a check valve. can get a pic of a check valve from work (designed for use with compressed air, but turn it around and it'll work for vacuum me thinks..maybe, will have a look tomorrow ) otherwise just get the check valve off a late model turbo jap car's brake booster system.... stops the air flowing back into the tank/booster, which you dont want it to do or the tank will be pointless and it'll mess with your engine etc
pic of vacuum tank on bros filthy 4wd 'lux
would be an easy as a mofo install job, hell, even sparkle/lowlancer would be able to think they could do it