Hobie doesn't publish their sales figures (no private companies do).
However we can make assumptions based on public knowledge regarding the industry. ( I'm in manufacturing)
It's published everywhere that in 2015 225,000 kayaks were sold in the USA alone. Hobie is by a wide margin the Cadillac of all kayaks on the market and likely the biggest market leader (Number 1 brand out there (bar none)), lets assume they own 25% of the US market (conservative estimate). Their mirage line of kayaks we all know is the vast lions share of Hobies kayak market, so assuming 225,000 x 25% = 56,000 kayaks sold times 90% = 50,000 mirage kayaks sold in the US alone annually. Every Mirage kayak Hobie sells (all lines (revo, PA, Adventure, sport, outback, Oasis, etc) are designed from the ground up as a sail boat, you only need to add the optional sail kit (about $400 bucks), and you have a full blown sail boat, designed from the ground up to sail (almost nobody knows this).
You spiked my curiosity, so I worked up the numbers 3 different ways ( financial disclosures, known rotomolding manufacturing capacities, and available factory space (and counting parking places in their facility (it's against the law to have more employees than parking spaces)). I put their output at right around 100k mirage kayaks sold globally annually. That number also coincides with their estimated sales revenue, assuming 60% of their EBITA business revenue is kayaks.
Assuming the kayaks last ten years, that puts the number of Hobie mirage sailing kayaks out there at around 1 million.
Now figuring maybe 5% of the owners get the sailing kit, that gets us to around 50k sailable mirage yaks out there. We have bought and owned 8 different Hobie mirage sailing kayaks over the last ten yrs, I would describe us as average hobie mirage kayak owners.
I'm out on the water most weekends, about half the kayaks I see in this area are Hobie brand mirage kayaks. I'm pretty sure there are around 200 Tandem Islands in the Sarasota area, (Sarasota is a small city just south of Tampa bay.).