Does anyone know where i can get an adaptor for a rhodes mk660...which i understand is the same as a Roland d-70 keyboard?

I would have thought the power supllies would be built into the synths, I am sure the D70's power is via the mains. If the MK660's power is via a "Wall Wart" Try contacting Roland themselfs to see if they can source one.

Most likely Roland has printed everything you need to know on the back of the keyboard. It will say something like 9v 400ma. This means you need a 9v power supply that puts out 400 ma. You can find one of these anywhere. But take heed, they also show on the diagram that the inside is positive and the outside is negative. Be 100% certain you've got that right before attempting to use another power supply. The manual will also have some info for you.

(just to be complete)

most adaptors have + inside and - outside. Boss and Roland almost always use + on the outside and - on the inside (it's on the back of your synth in a little diagram), so switch the wires.

If it reads 9V 400mA, you can also use 9V 1000mA or something, you just can't use less as 400, but more is no problem and it's not going to damage your synth, as the synths only uses what it needs.

You can actually power a 400mA and a 600mA synth at the same time with one 1000mA power supply, this way you can make one power supply for all your synths (If they all use the same voltage).