Hi Mark,
I'm just up the road from you, so if you need a hand looking at a few trucks, I'd be willing to call down and help out, if it suits with work etc. I've no experience with the TD5, but I've a fair knowledge of defenders.
There are 200 and 300 tdi trucks out there, you just need to hunt a bit more for them, than in the UK. My sister recently bought a 200tdi 110 and it's a great truck. Keep and eye on autotrader.ie and carzone.ie.
Also, if you haven't found them already, check out The Land Rover Club of Ireland
There's a guest forum there for non-members, if you want to post a Wanted for a truck. A few of them are on here too.
Hold out for the truck you want and you'll get it.