Rodriguez has long gone out of business so it's highly doubtful that you'll be able to find anything. The best alternative that I know of is Crunoz. I'm pretty sure that they source from the same place that Rodriguez did but their quality is better. Their max on 1st base mitts is normally 14" but you may be able to get the to do a one-off if you call & ask.
It's unusual to see anyone using a mitt that big outside of senior ball. In any case, the bottom line is use what works for you!