I take Estradiol sublingual and I have no problem getting refills. This is just one advantage of sublingual tablets.
For injectable Estradiol, just talk to your local Pharmacist. They may have to order ahead of time or substitute a different brand or strength. Hit or miss supply, is really just not good planning by your Pharmacist for the need of his customers. As long as they know you will be getting your Estradiol at their store, they can have refills waiting for you.