Bullpen rhymes with:
playpen, airmen, biogen, bruntjen, businessmen, canadienne, energen, euroyen, flagmen, gunmen, julianne, longden, mahen, mailmen, middlemen, minutemen, neupogen, nexgen, parisienne, playpen, powergen, repairmen, shenzhen, synergen, tiananmen, turkmen, uniden, urgen, valencienne, weathermen
Bullpen sounds like:
balaban, balbina, balboni, belvin, bilbaoan, bliven, bolivian