They are availiable, not sure where though or how much as I haven't needed one until now.
General census is that it's better to take your own depending on childs ages as the DLRP ones do not recline at all and you have to give them a substantial deposit to enable you to take the buggy's out of the park.
No DLRP don't hire out double buggies. The single ones are OK we used one everyday for my 4 and 5 year old girls to share, it was great for tired little legs. I think they cost 8 Euros but we got them free with our Annual Pass.
thanks all for the help i think it will be easier just to take my own buggy dont think i could face 2 little ones in an airport for 2hrs without being able to contain them anyway