Why not issue a proper TOURIST VISA / DOUBLE ENTRY in Thai Embassy in Croatia PRIOR YOUR ARRIVAL ?
If you were already here, there are some solutions such as travel to Thai embassy/consulate in neighbouring countries (Laos,Cambodia,etc) but it will cost you time and much money compare if you are doing it before arrival in your home country.
The tourist visa is easy to issue and not costing you much as well.
It believe it can be done and will save you time,money and headache.
*Visa Run by land will cost you much more and you will get only 15 days each time.
**Do some search on the forum.
Thailand Embassy , Croatia.Address: Verecke ut. 79 Budapest 1025 Hungary
Phone: +36-1-4384020
Fax: +36-1-4384023
Email: thaiemba@mail.datanet.hu
-----------------------Thailand Consulate , CroatiaAddress: Gunduliceva 18/IV Zagreb 10000 Croatia
Phone: +385-1-4830359
Fax: +385-1-4830359