Fargesia, Thamnocalamus come in a variety of colours, but not really yellow. S. fastuosa is very green; S. yashadake kimmei is very yellow, but not tall enough for you.

Most of the decently yellow bamboos are in the Phyllostachys family. As noted above, P. aurea is one of the best behaved in British conditions (but rampant in some other climates), but the standard type, most commonly sold, is not really yellow. But there are good yellow cultivars of it from specialists such as Koi and Holochrysa. P. aureocaulis spectabilis is a bit more vigorous with a somewhat more wandering tendency, but is probably also just the right size. Other yellow Ph risk getting bigger than you want.

By dividing, I was trying to save you money. Dividing does not promote growth, it sets it back initially. Yes, with larger specimens you would spread them further apart. Fully 3m specimens are available, but in quantity you might need to go to a specialist large specimen supplier such as tendercare.co.uk (Denham, on A413 at close by M40 J1). http://www.tendercare.co.uk/pdf/Tend...amboo_List.pdf Their 3m P. aureosulcata spectabilis, for example, costs £300 per specimen and come in 160 litre pots, which will doubtless weigh 300kg+, so you'll need major excavation and lifting machinery. Whereas I was trying to do you the whole job for the price of one of those: eg £300 you could by 6x 20l Fargesia plants from Jungle Giants, divide each into 3, and plant at 60cm intervals. Just have to wait a few years for full effect.

The other suppliers I mentioned do have a scattering of tall bamboos in (much) smaller pots, but will obviously be a lot less mature, and whether they can do quantity, well you'd have to ask.