I used to work at a kennel - it was quite popular but it made me never want to leave my dog.At this kennel no raw/homecooking was allowed... And if you brought in your own kibble, although they said that was fine, they'd actually feed the kibble they stocked. They also cut the dogs rations in half so they wouldn't get chubby (necessary since the dog's only exercise was in a small run while the cage was being cleaned!).
I think a lot of kennels do not allow raw feeding because of possible guarding issues, choking on bones and the risk of bacteria affecting the other dogs. Also, any dog on raw would have to be watched to make sure they chew the bones properly - I certainly wouldn't want my dog left unattended with a bone... All of that takes more time and effort (not to mention the "risks"). So in a way, I can see why most kennels refuse to feed raw (although I certainly wouldn't be leaving my dog at one that didn't LOL...)
You may want to try your vet if he/she supports the diet.
You could offer to pay extra for the raw feeding.
If you got your dogs from a breeder, you can see if she/he would help you out. Or you could even try any local breeders that feed raw - they might consider it for a price of course LOL
You could allow them to feed raw patties instead of asking them to supplement and give bones etc...
But by far, the best route IMO is to try and find a dog-sitter, friend or family member that can watch your dog. Even though my dog would be completely understimulated, I would much rather leave him home alone 22-23hrs a day than leave him at a kennel... Even if I thought the kennel would take wonderful care of him, I know he would be a lot less stressed if someone familiar to him came in and took care of his basic needs at home (assuming that this is only for a short period of time!)
If nothing is looking promising, the only option you may be left with is switching your dog back to kibble a week or so before boarding