Legendary Canadian caver Mike Boon passed away in 2014, but portions of that '65 - '66 Jamaican expedition are documented in his book Down to the Sunless Sea
, available online at this tribute website thanks to the Alberta Speleological Society: http://www.caving.ab.ca/boon
The NSS Library
shows a copy of the full report on file, which you may be able to access.
Or, you may have luck contacting also-legendary karst hydrogeologist Dr. Derek Ford of McMaster University, who led(?) the expedition. The University's website lists his professor emeritus email address as `dford at mcmaster dot ca
`, though I'd recommend checking the NSS Member Manual as well.
Finally it never hurts to contact SpeleoBooks
when searching for rare books of this sort.