If you are chasing a bolt in replacement, You need to find an original one. The 1k has a very low profile engine bay, so most radiators are too tall.

Pretty much everything will require you to modify the radiator somehow.

I have a couple of 1k tanks and straps if you get desperate

So far you have a choice of early corrolas, gemni, 1200

I have heard of people using hyuandi excel ones...

I know exactly how you feel! my original radiator was a bit batered to say the least, as mentioned before the 1000 has a small profile on the engine bay, you'll find that most radiators have to be modified to fit, Just take some measurements and go down to the local wreakers thats what i did, a little leg work wont hurt you! you never know what you'll find. I used a corolla radiator, not exactly sure what model. to fit it i just used 5mm flat bar and ran it from the bolts in the radiator support to the holes in the radiator, i used good quality nylock nuts and stainless steel bolts, its not hard just takes a bit of commonsense.