No, there aren't. But don't take my word for it. See for yourself.
List of English Irregular Verbs
- For Teachers
are there any irregular verbs that start with the letters, "j,n,v,x,y,z"
You might be able to form one with a prefix or something, but I can't think of any.
But our list is complete, including those irregular verbs starting with out-, over-, pre-, re-, un-, and under-.
I bet there is one out there somewhere, hidden away in the darkest recesses of the OED, unused since 1728.