Most of the polled bulls are heterozygous.  In other words, if they are mated to a horned cow, only 50% of the offspring will be polled.  However, there are a few homozygous bulls available.  If you see a bull with the -PP designation, then he is confirmed homozygous.  I have been using Dallas-PP for almost a year now and every calf has been polled.  Dallas is available from Coba/Select Sires.

The NorthCoast Group has several -PP bulls available.  I think that Michigan Livestock Service will have a -PP bull available soon that has tested positive as a carrier of the very desirable A2 beta casein gene.

So, yes they are available, but it may take a little searching to locate.