You may not be able to find a dual-sport boot in that size, but there are boots available.
Alpinestars Tech 3/Tech 5, Thor Ratchet, Tourmaster Solution, and Fly Maverick are made in sizes to 15 and 16 and in the price range.
Except for the Solution, these are MX boots and may be a bit stiff to walk in, but the protection is there. The real difference between an MX boot and a dual-sport boot is that the DS boot may have a bit less crush protection in order to be better for walking around in.
A budget of $200 should be enough to get a boot of pretty good quality, too.
I don't know how widely available the larger sizes are, but BikeBandit seems to carry them
They are a pretty good outfit and seem to have a generous return policy on stuff, which you're probably going to need unless you can find a brick-and-mortar where you can try them on before buying.
I've bought plenty of stuff from them and haven't had a bad experience yet, but I haven't had to return anything. When I bought my Gaerne Explorers (I have wide feet; only boot I could find at the time that was reasonable priced that came in wide sizes) the fit really well out of the box.
Open up a chat session with them and ask which boots are likely to fit your foot length and width.
The work boots will provide good sliding protection but you could wind up with serious ankle/foot damage if you get caught in a foot-crushing situation. No protection at all with those.