Want to buy stainless JBA shorty headers
 

for 2005 hummer h2

can be used or new

you can buy them from the JBA site. they are a bit cheaper then summit racing or jegs
but rockauto has OEM GM manifolds much cheaper.
the shorty headers will not make an improvement over stock manifolds if thats what you where thinking. header flanges can also warp or crack welds with heat cycles.
if you where looking for more gains over stock then you need to consider long tube headers. short tube no gains over cast iron.

if so many people are saying the iron headers crack/leak, it would make sense to upgrade to stainless from that perspective i guess, so was looking to buy a used or new pair for less than JBA website price

is there a part number for the flanges? or do they come with new headers?

you would have to ask JBA.
if the cast iron heads crack it is usually because of broken manifold studs or bad motor or transmission mounts. normaly they do not crack "willy nilly"