I don't know if there already is one, but if there isn't, there should be a request board. Where people can request random things, like things that need to be shopped, sources of specific pics, etc.
DubiousCharms has a photoshop request shoppe, where she takes requests and pictures and details of what people want done to them, but there are rules, so it depends what you want shopped.
Take a look in that forum to see the rules, etc.
Here's the link - http://www.animegirldesp.org/forum/index.php?topic=3217.0
Apart from that, asking for sources of any pics you see, I guess you just have to ask.
There should be nothing wrong with asking for the source of pics either in the thread they were posted in or by making your own thread. At least, not to my knowledge.
As for 'shops, the only one willing and able to do shops at this time is DubiousCharms as Tru has become far too busy and DC has her own board for just such an occasion.
If anyone else with good photoshop skills wants to offer to do a lot of shops, they need only PM me with a request for their own board.