I've also tried to obtain but the various ones I saw, whilst the spaces between the six individual rings were correct, the spacing between the two sets of three rings did not match what was needed. I tried ENSONS (manufactured the springs for Michael Gouby's binder) but no go. I contacted M.G. to see if he had any spare binders or could direct me to where I could purchase one but, again, no go.
M.G. informed me that he had tried to obtain some "spares" but his printer informed him they were no longer in production, although he'd found one box of 300 ring springs in Italy that could be bought for £1000. Transpires this six ring spacing was the one used by File-O-Fax but went out of production 10 years ago.
Would be interested to learn if anyone does manage to obtain any!