They are out there, couple current ones from custom guys like Arlan,(not sure he is making calls anymore) but most are classic calls from many many years ago.
I will say though, that the external tone board type that is most common today, is common for a reason, and that is because they were designed back in a time when crow hunting was very common and popular (20's to 60's etc). Almost as much as waterfowling is today. A caller needed to be able to pull the toneboards, and clear any spit or debris out of them then put them back in quickly so he could get back to calling. You could also tune them for more or less rasp very quickly.
The types that were designed to be internal (enclosed reeds style) just were not easy to
take out and maintain, thus faded in popularity. Just to difficult to deal with.(made from wood, the toneboards or "guts" could get wet with moisture and swell making them impossible to remove)
Also, the external type that is preferred by most crow callers today are able to be used as a hawk call by blowing sideways thru the toneboards. Usually one side is better than the other.
Unfortunately,the toneboards set used by most custom makers today (Pioneer) are not really good for this as the gap is to wide. These are really made for turkey locating and not hard core crow calling.
Mark