Can I get any caliper from any disc brake and – assuming I can deal with the hose – attach it to my formula oro lever?
I want to replace a caliper I can’t seem to replace the seals on successfully and can’t find a cheap oro caliper or brake to buy to use. I would use one that uses similar brake fluid

TIA

Have seen some bodges like this work, don’t think there are any guarantees tho. Don’t mix mineral oil and dot fluid parts I think.

Maybe, but it also might not work at all. Just buy a deore brake instead.

yup have done this, as Cynic-al says make sure you get a caliper for the right fluid and it will be fine. Formula use dot 4 and or 5.1 (which you can mix, just do not use dot 5 or mineral) so any Avid brake will work.
Superstar do universal connection kits.

You need to make sure the lever pull/fluid pushed is enough for the caliper you are working with. Could be quite hit and miss really. What are you trying to repair?