Nope @Zdeněk M
you are stuck on the verification method offered you in your dashboard by GoogleMyBusiness.
But read the below general advise:
You are supposed to request th
If you have been waiting more then 14 days for a postcard then your best option would be to contact business support
I recommend getting in touch with GMB support via one of these options and ask for help in getting verified:
Helmut Geissler, Google My Business Top Contributor | my G+ profile