The Pets At Home nearest to me doesn't stock it. Can't understand why as they stock Royal Canin cat food but none of the dog ones.
The pet shops in the two little market towns near us don't have it either, but you may get if you're near a big town. But, as I said, my village shop gets it for me. The owner has no problem, I ring him to order it & he picks it up from his wholesaler. The Royal Canin Yorkshire only comes in  one & a half kilo bags now. I used to be able to order a small sack but the wholesaler doesn't have it now, so i buy 2 of the smaller bags at a time, they cost £7.50 each &  a bag feeds one Yorkie for about a month. The Mini Junior comes in a 3 kilo bag & costs nine pound something, not sure  of the retail price exactly as I've only recently started to use that & bought it from the Royal Canin stand at Blackpool show. 
Yes, you're right about sticking with what the breeder has been feeding at first. It's enough of a change moving homes without risking a diet change as well, but you can gradually move her onto the new stuff over a few weeks.
Bet you're excited!
 
Have they been born yet?