We bought from Baker Creek Heirloom Seeds. [0] They show to be out of stock at the moment. This is probably the best source for rare vegetables, herbs, etc that we have found. Their stuff actually grows too whether you buy a live plant or a package of seeds. Germination rates from seeds we have purchased from BCHS beats similar seeds from other sources like home garden centers all day long.

[0] https://www.rareseeds.com/crocus-saffron-25-bulbs

We have also bought from an online seller through Amazon and had similar results with the bulbs we planted. After our success, several relatives have also bought saffron crocus through BCHS or an Amazon link and will be having their first harvest this growing season. There are some Amazon sellers who still have some available. [1] It will also be pretty widely available in the fall from other heirloom and organic seed and vegetable sources since it is typically planted in fall so it can over-winter outside.

For us it did not matter that we added to our plantings in the spring last year. We had an unusual cold snap that kicked them into gear and the summer was hot and dry. It was great.

[1] https://www.amazon.com/saffron-crocus/s?k=saffron+crocus