Aside from the 1,000,001th suggestion for KEH, i'd shop zBay and see if Igor's Camera has anything in these focal lengths. I bought my 65mm C from them - rated as "Good" condition and it is like new - absolutely perfect and a great return policy as well. I'd buy from them without hesitation.
KEH has had a supply of "LN" 90mm and 127 K/L lenses for at least a year. They grade 'em as "LN", but from what i've read - aka RUMOR (from seemingly excellent sources) - the lenses are New, but sold as "Old Stock" to KEH who supposedly bought Mamiya's entire remaining RB lens inventory. I noticed them when i began building my RB67 Kit. I'd followed many, many threads about C vs K/L and opted for C, but a nice, "LN" 127mm sure is tempting.