A lot of the fields were (for a variety of reasons–see Charge Back Black List, if you want to know “why”) taken off of Gumroad.
But they are still available, just not on Gumroad.
I thought you had been directed to this thread (Temporary Invoicing for Gum’s Med Fields) but if I’m mistaken and you had not yet been directed to this thread, it will tell you how you can order this field.