In order to reach over the 'lip' of your fuel tanks (and if the ladder is to be made of aluminium) the bottom of the steps will need to be weighted so that there can be a 'mini-platform' jutting out over the tanks for your technician to have some space while re-arming the dispensers.
We have aluminium-works in Italy which could put something like this together in a matter of hours.
However, try Semmco (above) to begin with (and who are located in the UK), they supply Bristow/FBH, and see if they will create what you want and give you a fair price.