Having leylandii can be a double edged sword, as you have found out, Aptuspm. Leylandii can be a real pest of a hedge, especially if it is your neighbours, but when it is removed you privacy goes with it.
As for buying mature bamboo IO think that the idea is good and would suggest that you do a web search to look for a specialist bamboo nursery in your locality. Mature bamboos are large and transport will not be cheap, also I would suggest that you should see what you are buying before parting with your money.

i got a black bamboo this year about 7ft but not to busy at moment, but it will be expensive if you get a bigger one, £40 for mine, so bigger will be alot more, as bulbaholic says transporting will be dear to, better to see them also,

there was an old lady who swallowed a fly i dont know why ........................... i would think about a lot before buying any bamboo .transporting it any distance of any size will cost you but i think that could be the least of your troubles if you get the wrong one or do the wrong thing with it.it grows realy quite quickly but the wrong type will grow everywear at theplaces quickly.you can get a special membrane for bamboo that sends out suckers thats 60cm wide and you have to bury to within an inch of the top .ie burying about 57cm into the ground all the way round with know gaps wear you want your bamboo to grow.the up side is you can split bamboo and make more than one and send new suckers in the right direction .if you keep it in tubs above the ground it will break them eventualy.i use the membrane or i get a big strong bucket/nylon dustbin and ut the bottom out and bury it .the earth surounding the bucket then stops it splitting the bucket and as they slope out the shoots or suckers tend to come upwards and both have worked well for me.the other option is clump forming bamboo but i dont think that will do the job anywear near as quick.

the soil will be terrible to bye the way so it would be a great time to dress that to which you will have to do anyway if you want to grow most things but tumble weed and the odd cacti and predetory plant lol.