You can find Tylan powder for the water online without a prescription from some pigeon sites. Some have run out due to the demand, but you may get it here:
https://www.nepigeonsupplies.com/product/tylosin-powder/
Dosage is 1 tsp of powder to each gallon of water for 3-5 days. Only add water to...
Jedds also sells tylosin (Tylan) powder, but it is out of stock. But this place also sells it:
https://www.nepigeonsupplies.com/product/tylosin-powder/
Dosage is 1 tsp per gallonfor 3 to 5 days.