Core plug problem

My 1990 Jeep Cherokee Laredo, has started to overheat (pretty much like everyone elses by the look of the forum) but mine seems to have taken to blowing the core plugs out and emptying the coolant.
How do I stop it doing this
and where do I get replacement core plugs from, with it being a 1990 canadian import, the local dealer (merc/Jeep) reckons they can only find these parts by giving the engine number, which they don't recognise

Are you talking about the freeze plug? My '96 Cherokee has repeatedly blown freeze plugs due to overheating and emptyed coolant leaving me stranded. I got several rubber expansion plugs from NAPA. I don't know the answer. I'm sick of it! It has been a wonderful vehicle otherwise. Search internet preformance parts sites, those that carry engine rebuild kits also usually carry freeze plugs.