Benja,
I happen to have most, if not all, of the pictures you mentioned.
The "Art by Rob" collection was posted many years ago on a now-defunct enema newsgroup which -by the way- I never found really interesting, so after awhile I quit visiting it so I don't know whether the original collection was actually larger than mine. The only point I'm sure about is, I remember they didn't came from a Yahoo! group. From what I can recall, I found them on the original (i.e. not Zity's) Canadian forum "Les plaisirs du lavement".
There are seventy-four pictures in my own «Art by Rob» folder. I may send the whole Zip/RAR compressed folder to your mailbox. Then you might as well post 'em in the Gallery if you feel like. To tell the truth I really never liked it, my own tastes being somewhat more refined than such stuff. IMHO these photomontages boast quite a bit of bad taste and I found some of them being plain vulgar, rude and the like.
I understand they may be appealing to some people though. Since I've long been involved with enema related research and documentation from all over the world, I saved them mostly for completeness' sake.
==quick edit==
I just forgot to mention some other montages I downloaded and saved from the same site, definitely more humor laded and smile-drawing. These are fifteen «Enema» magazine plus two «Ladies' Home Nursing Journal» and one «Mothers' Enema Symposium» cover spoofs.
Funny thing, the «Enema» magazine's covers sport (phony) bar codes although pretending to be issued during the Fifties...
Let me know about it, anyway... I'll be eager to share them all.
Cheers!