Defra have their own list, see here this is as at 16/11/09.
http://www.defra.gov.uk/foodfarm/policy/animalhealth/vservices/ultrasound/scannerslist.pdfThere is someone in Berkshire but not sure if they'd be willing to scan dogs.
Might be worth contacting them?
However there is one person on the list that does scan dogs too
Mrs Samantha Wilkinson, she scans at Wey Farm Kennels Nr Guildford on I think it's a tuesday.
She will come to your home for extra fuel money. I had her do my bitch twice and it cost £150 for the two times
for her to come to my home (Berkshire). This was 2 1/4 years ago. However if you go to the Wey Farm Kennels it is cheaper.
Not sure what her prices are now though.
She was spot on with numbers. We had the bitch scanned twice as she advised that she thought the bitch was losing puppies
and to get her a course of antibiotics. Which we did and she only lost one that Samantha saw on the first scan.
Which is why we were also able to save the last pup and got the bitch a c-section after she had shut down, seemingly finished.
My own vets scanned again to make sure..and there the pup was.