there is no mod that directly covers your request, but there is a way i found that gets around having to find one (which from personal expierience is very hard). just download the GUI spawner mod which allows you to change what comes out of a mob spawner. the simplest way of doing so is inventory editing yourself a mob spawner w/ any sort of INVedit program, creating a grassy area (grass not dirt, because any peaceful mobs,cows,sheep,wolves,ect., can only spawn in light, grassy areas) then ploping down the spawner and changing it to spawn wolves. if you have any questions on installing the GUI spawner mod, PM me and i'd be more than happy to help you out.
GUI spawner:http://www.minecraftforum.net/viewtopic.php?f=1032&t=80246
GUI spawner:http://www.minecraftforum.net/viewtopic.php?f=1032&t=80246