Rangpur lime seeds are available on ebay. They come in 50 and 100 seeds packages at a reasonable cost. The seller ships from Brazil, therefore an agricultual permit is required. There is no way around the permit due to the drug traffic from south america.

Import of any seeds from Brazil is strictly prohibited by federal law, and permits for such are not available. Here's the exact quote from USDA regulations:

"Citrus family (Rutaceae), seeds of the following genera are prohibited from countries infested with HLB and CVC (seed-borne diseases of citrus): Aeglopsis, Atalantia, Balsamocitrus, Bergera, Calodendrum, Citrofortunella, "Citroncirus, Citrus, Clausena, Fortunella, Limonia, Microcitrus, Murraya, Poncirus, Severinia, Swinglea, Toddalia, and Triphasia. Countries infested with HLB and CVC are Argentina, Bangladesh, Belize, Bhutan, Brazil, Burundi, Cambodia, Cameroon, Central African Republic, China, Costa Rica, Comoros, Cuba, Dominican Republic, Ethiopia, Eritrea, India, Indonesia, Japan, Kenya, Laos, Madagascar, Malaysia, Malawi, Mauritius, Mexico, Myanmar, Nepal, Pakistan, Paraguay, Papua New Guinea, Philippines, Reunion, Rwanda, Saint Helena, Saudi Arabia, Sri Lanka, Somalia, South Africa, Swaziland, Taiwan, Tanzania, Thailand, Timor-Leste, Vietnam, Yemen, Zimbabwe. Seeds of these genera from other countries
can only be imported into the United States if, upon arrival at the first port of entry, they are accompanied by an import permit and a phytosanitary certificate from the country of origin, with an additional declaration stating that the country where the seed for planting was produced is free of HLB and CVC.
Seed of citrus genera that are not prohibited require a written permit and, if from countries infested with citrus canker (listed in 7CFR319.37-6), a port-of-entry treatment."

Since Brazil is an HLB and CVC country, they won't permit it.

I ALSO FOUND IT DIFFICULT TO INPORT RANGPUR LIME SEEDS. I ORDERED THE SEEDS FROM PORTUGAL. THEY ARRIVED IN 5 DAYS TO HAWAII. Go to Ebay.co.uk and you will find it there. The seller is an exceptional person from Europe. Humble, sincere. and honest. He sells it by six per package.