Of course the D40 isn't a ring flash ... Marcus asked: "Are there any other, more portable, flashes for the V cam? Not necessarily ring".
By far the best ring flash I've used is the Hensel which is made of carbon fiber so it is very light to hold, and has a handle for hand-held work in studio. As far as I know, none of the pro level, larger ring flashes are self contained and mobile ... they are tethered to a generator box.
The smaller, self contained ring lights available for 35mm cameras, and often used for macro work, throw a small circle of light, are underpowered and wimpy.
Ring lights work because they surround the lens and light fairly evenly, often producing a tell tale drop shadow around the subject and a donut spectral highlight in the eyes. The effect would be lost with a reflector made for the D40.
I suppose you could make a "beauty dish" reflector for the D40 using the Telephoto reflector and adding a center "dot" with a reflector surface facing inward. But I doubt it'd work since the shape of the tele reflector is designed to narrow and focus the light beam.
I have been searching for a new D40 for some time now, and I strongly suspect that it was discontinued. The large online stores in North America haven't had it listed for ages now, in general all there is the remnant stock of associated accessories. It may be possible to find one used -- KEH lists them fairly regularly -- but I would be leery of buying a used flash since one never know hard it was used (at is was/is popular with wedding photographers) and whether its capacitor(s) will give up the ghost shortly.
If you want a new one, you may want to check out local stores that sell/sold V series gear as they may have one collecting dust. Keep at it whenever you pass such a store in your travels and you just never know.
Is it possible to use the Nikon ring-flash (r1c1, sb-R200)on the 5O3 in the A-mode so that I can use this for macro ??
I also would like to know. The SB-800 works in A mode but I don't think will control the sb-R200's. I think the SU-800 would work but I don't have one so have no experience. Nikon now lists an SU-4 control unit which may allow the use of SB-800 and the SB-200.
I would be interested to know if 503CW+SU-4+SB-800+R-200 would work. The SU-4 is $75 and the SU-800 if $250.
Correct, the SB-800, alone, won't control R-200's. I am wondering if a SB-800 in auto mode and with sync cable from 503 will control R-200's if used in combination with the SU-4 controller. (This question is pretty far out in the weeds *g*.) The "real life" use would be using the R-200's as a ring flash for my 120 Macro.