Ladder for van bunks

hi, we are after help.We want a ladder for our bunks in our new van. We opted to not have the built in timber ladder as we knew what our youngest child would be like!!! The ladder that has been provided to us is of no use - it i a yachting ladder that folds in on itself and doesn't stay straight. We have the okay from our van maker to find one ourselves and we will be reimbursed, which we are happy with. Does anyone know where we might be able to find one?? Space from top bunk to floor is only approximately 125-130 cm, we would prefer aluminium so it is light weight.

any help would be greatly appreciated.

thanks so much,
Darren and Lisa Robertson