I did a fair bit of research looking for a lamb for our wedding picnic. One option is a number of greek restaurants will do a baby lamb for you, but they do not roast on location. (same with La Unica for pig, see this
thread)
We ended up having a roast lamb prepared by Farmer Smith (a pig farmer from Plano IL) and his family. They have roasted pigs for the Chicago Beer Society events in the past and did a lamb for us. The receipt from july 03 shows a charge of 160 for one roasting lamb (53 pounds dressed), 395 for cooking and equipment, 25 for travel and 25 for generator rental, for a total of 595 for the lamb.
Griffin will correct me if I am wrong (or maybe any other CBS member who is lurking) but I think they roasted a pig for a neighbor once, and word spread from there. This was years ago. By the time of our wedding they were routinely doing CBS events and were booked with atleast one roasting each weekend all summer.
Farmer Harold has passed away I think but I think the family is still in the roasting business. I think they still did our pig on the CBS beer (brews & blues) cruise last year, and it was actually a son in law (Bob) who came out and roasted our lamb.
Bob used lemons and a very nice mediterranian rub -- it was his first lamb and all agreed it was wonderful. We even knocked a vegetarian off the wagon with a little lamb organ meat!
The number for Smith Farms is 630 552 8452.