Hello fellow AFOLs, THack here – obviously new to the Forum. Been lurking for a while & thought I’d join the party. Primary Technic Fan; but an all around AFOL. Hope to participate in the conversations & enjoy the camaraderie of AFOLs.
-THack-
There's always the option to use Lego Education > Lego Spare Parts and procure what you really want: http://www.legoeducation.us/eng/characteristics/productType~LEGO%20Spare%20Parts .
Take a look and you'll find Pneumatics parts & small kits (e.g. http://www.legoeducation.us/eng/product/pneumatics_parts_pack/2020 ). This way you can get what you're looking for and use you're current sets to build / create from.