How do I get bait?

Not sure if you can buy it anywhere but you can make it. You might need to finish the autumn forest fishing quest first.

Use the make option in the bottom left and look for various bait items to make. eg meat fish bait.

You can make them. After you finish the fishing quest in the fall forest, you'll get a formula for lv1 fishing rod and 3 bait formulas. Metal bait, meat bait, and vegetable bait. Then the quest will continue to Farstar City. Finish this to get lv2 fishing rod formula and to unlock the next quest, which will give you lv3 fishing rod formula and allow you to get the 4th bait formula, shrimp bait.

If you have joined a camp, you can go to the camp pond and buy them from Murong. He'll sell the first 3 kind of baits for 25 camp contribution points, and a special yeast bait for 25 contribution points plus 3 fed credits each.

While there is no limit on how many bait you can make daily, as long as you have enough materials, you can only buy 50 of each basic baits and 20 special baits in a day.