Hullo - I just thought I'd share my husband's photos of Carter's Steam Fair, which came to Bath last weekend.
Carter's is indeed a mostly steam-powered fair, and travels mainly using a fleet of vintage Scammell lorries - one, 'Why Not', has been on the road since the 1940s. I'm pretty sure it's the largest and most diverse fleet of Scammells in the UK.
Quite a few of the rides date from the early 20th century, although many look older as they're decorated in a traditional funfair style, so I'm guessing that they'd be more of interest to steampunks than dieselpunks. I got very excited by the chair-o-planes as I've seen them in lots of 20s films! However, there was an authentic Wall of Death in which one of the riders rode an Indian Scout imported into the UK in 1929.
(I've blogged about it too, but my photos are just nicked from Pete, so if you just want to see the pretty pics, the top link is the one to use.)