CROATIA and the Road to Duibrovnik

(this might be a repeat - new to this)  GREEN CARD INSURANCE we wanted to take van to Dubrovinik but have to drive 22KN along road in BOSNIA to get there-  Taken out new insuarance with Caravan Club Scheme told cannot get Cover for Bosnia only from AXA at very high cost, cancelled.   Gone back to SAGA renewed insurance told they cover Bosnia but then told they cannot insure / issue Green Card. Would anybody know who will insure a sensible cost ?  Dont want to use ferry.  Told can get temporary 3rd party Green Card cover at boarder,  has anybody experienced this ?  how much ?  is it easy to get ?  can you get in advance from who ? how much ? (is PD reading this !)   Understand many going to Dubrovnik but do they actually worry about cover ?  somebody help or will go to Italy instead