At first I was thinking some standard bolt would work, but after looking at your pic I can see that won't be the case. About all you can do is look for a junkyard with a truck in it or find someone willing to part with them. You'll be looking for a 72-75 LUV truck (or the motor/parts from one) and later models (76 and up) will not have those same bolts. I have a complete head from one of those early year trucks, but I'd rather not pull parts from it. Could be someone else from here will have some parts laying around from after their V8 swap and could help you out too.
When I get home I will check the parts book and post up some Isuzu/GM part numbers for you. You could then check with dealers in your area and see what they can find. I have been highly recommended to the parts department at St. Charles Isuzu as they have some real wizards working there and treat online/phone orders very well. Check them out at
http://isuzu.stcharlesauto.com/Department-Parts.aspx
The person to talk to there is called Merlin, and many of the Isuzu people I know swear by them for hard to find parts.