The Pacific Bulb Society - a nonprofit that has seed and bulb exchanges available to members several times a year, must be a member to participate
Rare Plants Nursery, United Kingdom Shipping is expensive, the plants are as advertised and always arrived for us in excellent condition
Illahe Rare Bulbs This one is tricky - they offer their catalog once a year, in late July into August, for a few weeks only. Often have excellent prices, quality is spectacular, and Mark is communicative if you need support or have questions. The old catalogs are posted for archival purposes - and the blog format to find the catalogs when posted is confusing, at least to me.
Seeds of Peace - Oron Perri runs this seed and bulb farm in Israel. He generally grows everything - the seeds and the bulbs. Often has several species unobtainable elswere. Quality I've received is excellent uniformly, seeds arrive in a week or two typically.
Telos Rare Bulbs - a California operation, catalog lists items when available, so order right then if you see something. Diana has always shipped me very high quality plants. One of my longest running an favorite rare bulb sources!
LIBERTO’s SEEDS AND BULBS Eleftherios Dariotis growing bulbs near Athens, Greece - I've always had excellent interactions and high quality materials from him. He sells on eBay sometimes, and directly other times. He also produces an annual catalog he emails out in Summer. You have to email him at eldaebay at yahoo.com to get on his email list. Ask him about Biarum - he may have some not in his catalog due to small quantities being available.
If you know other sources, please make a comment and I'll update this list.
To obtain a "Permit to Import Plants and Plant ProductsRegulated by 7 CFR 319 Subpart - Plants for Planting" from the US Department of Agriculture go here and apply - they are free and enable legal importation of foreign plants (PPQ 587 is the form you are looking for):
https://www.aphis.usda.gov/aphis/ourfocus/planthealth/import-information/permits/plants-and-plant-products-permits for overview of the permit process
https://www.aphis.usda.gov/library/forms/pdf/PPQ587.pdf> for a blank permit form you can fill out in your browser and print to send in. If you are going to do a lot of permits, you can get put into the online system for applying for and managing permits - you have to take your passport into the USDA and make an appointment and all that.
It all begins with a flower... or is it a seed... which comes first, the flower or the seed? Er, yes, the seed came first, perhaps by a hundred million years. Happy gardening!