Try a dealer; Ensign are good shout. Your best bet would be early low-floor models such as Pointer Darts (by which I mean the original Pointer model seen in 'P'-reg Darts and not the more common Pointer II model) and - Heaven forbid - Wright-bodied Lances.
As I understand it this is only half true. Non- low-floor vehicles will still be permitted, providing a low-floor alternative of the same mode of transport (i.e. bus in this case) is available. This means you could in theory alternate between low-floor and step-entrance on one route.
I've done a lot of work recently with DDA legislation, and EVERY bus on a standard public service MUST meet full DDA regulations by 2015 for single deckers under 7.5 tonnes (effectively mini and midi buses), 2016 for single deckers over 7.5 tonnes, 2017 for double deckers and 2020 for coaches. The only way step entrance vehicles can be used is if tickets are pre-purchased from an office on an excursion/private hire/ historic tour etc.
There's a lot more to to DDA regulation than a vehicle being low floor with a wheelchair ramp too. Wheelchair bays have to be of a certain minimum size, deployed ramps have to sit below a certain angle, aisle width through the bus has to be of a minimum width, and the slope up in a bus has to be under a certain angle. Then there's the "silly" little things like all grab rails have to be a bright colour that contrasts from the rest of the bus, stop buttons have to be able to be pushed by a hand instead of just a finger or thumb, front side and rear destination displays must be in place and be operational with DDA font sizes, destination equipment must be illuminated, and then there's other things like if you start a new route you have up to 21 days to get destination equipment prorgrammed or printed for the route, broken destination equipment must be repaired within 21 days from the first fault reported, buses with broken wheelchair ramps aren't supposed to leave the depot until they're fixed, kneeling suspension must be operational, and special driver training has to be provided to ensure the driver is aware of correct safety procedures for safe use of the ramp, safe manouvrability of a wheelchair on board, guiding a blind person to a seat, and asking passengers to move to different seats to allow a disabled person to use seats at the front of a vehicle.
Generally, anything built before the end of 2000 will not meet the full standards, and will not be DDA certified. Operators can convert older vehicles to meet the full DDA standards and have them certified as DDA compliant for use beyond the deadlines, but if you think about it, when the deadlines come into force, non-compliant low floors will be 15-20 years old, past their economic life for public bus services.
