The parts sold at a hardware store are not nearly heavy enough to do the job of turnbuckles- you can buy them on ebay or from places like Weavers, or I can build you custom telescoping stabilizers. But, believe me- I've made them for many customers who attempted to use fencing/hardware for turnbuckles. They just aren't heavy enough.You might try this salvage yard
http://wkytpstore.com/
The turnbuckles could be cobbled together with parts from the hardware store.
You may also try to find out what (non gray) tractor is similar to the L1805 by asking. I do not know but it may be a L185, L225, L345 or something in that line (the L175 is equivalent to the L1501 I think) . Generally posting a picture of your tractor can narrow it down quickly.
Once you know that you can get the part numbers from the Kubota website parts manual.
Thanks for that link. I have been thinking about increasing my cooling capacity. Will have to check them out later.