I have so far refrained from commenting as I do in fact sell RAF and Regimental ties as a (very) small business venture, and didnt want to be accused of advertising. I did ask my own supplier/manufacturer who confirmed that they stopped doing the nav tie some years ago, although they do still supply the "standard pattern" and pilot's tie in silk.
Incidentally there are some optimists out there. I have on several occasions been asked to confirm that the polyester ties which I retail at £9.99 are made of pure silk! Don't know what you've been quoted sidevalve, but if it's under £25 you are getting a good deal For myself, I reckon my polyester nav tie which I've had for about 30 years will see me out!