heres the sales brochure i found online, mine are the LS3 but I have the optional 3rd piece which is the 18" woofer in box...
http://www.gray.mb.ca/fostex/RWO-FOSTEX LABORATORY SERIES MONITORS.pdf
this would be a good post for the above thread does size matter
I'm confused. What do you mean by you have the third piece? The LS3 is a three way with a 40 cm woofer which is just under 16 inches.
I suspect you are out of luck, as if there no more re coning parts, those speakers are boat anchors.
Those speakers are very high sensitivity so using some type of professional woofer might work. However the Thiel Small parameters and acoustic response would have to match exactly.
Do you have one working woofer, so the T/S parameters and acoustic response could be measured?
It is possible that JBL might have a woofer in their range that would match if the above information could be obtained. May Be Fostex can provide it?
I suspect that we will be looking for a vintage driver from JBL, Altec Lansing or Electrovoice. This will be a tough one as this is a high efficiency driver that tunes down to 30 Hz and can be crossed over at 800 Hz. This is going to be like looking for the needle in the proverbial hay stack.
However if you want to put a lot of time money and patience into it you might get lucky. However you need to be prepared to waste your time and money. This will be a gamble.
I have been on the Fostex site and their current 16" driver, W400A-HR, is nowhere near sensitive enough and only tunes to 40 Hz not 30 Hz.
I can't find the specs for your woofer on the NET. See if Madisound know or if Fostex have records. If there is a new driver with those sort of specs you likely need it likely will run over 2K. The driver I referenced above is 2.5 K. Good vintage drivers of the type I suspect we are looking for usually start at $350 at least and many I have seen go on eBay at around 2K a pop. Bidding is always fierce for the good ones.