I colleague of mine put together this list of providers of heirloom seed.  I can’t vouch for the links, so if you find any that don’t work please let me know.

http://www.2bseeds.com/
http://www.abundantlifeseeds.com/
http://www.agtoseeds.com/
http://www.amishlandseeds.com/
http://www.annapolisseeds.com/
http://www.anniesheirloomseeds.com/
http://www.aravaipa.com/
http://www.bbbseed.com/
http://boondockers.sharepoint.com/Pages/default.aspx
http://www.botanicalinterests.com/
http://www.bountifulgardens.org/
http://www.clearcreekseeds.com/
http://www.clearskyfarm.com/
http://www.cooksgarden.com/
http://www.companionplants.com/
http://comstockferre.com/
http://www.dianeseeds.com/Index.html
http://www.dirtworks.net/
http://ecoseeds.com/
http://www.eonseed.com/
http://www.eternalseed.ca/
http://www.fedcoseeds.com/
http://www.filareefarm.com/
https://www.gardenmedicinals.com/
http://www.ghorganics.com/
http://www.gourmetseed.com/
http://www.goodwincreekgardens.com/
https://www.grannysheirloomseeds.com/index.php/
http://www.growitalian.com/
http://www.groworganic.com/
http://www.harmonyfarm.com/
http://www.heirloomacresseeds.com/
http://www.theheirloomgarden.com/
http://www.heirloom-organics.com/
http://www.heirloomsevermoreseeds.com/
http://www.heirloomseeds.com/
http://heritageharvestfestival.com/
http://www.highmowingseeds.com/
http://www.hometownseeds.com/
http://www.horizonherbs.com/
http://www.humbleseed.com/
http://www.italianseedandtool.com/
http://www.irisheyesgardenseeds.com/
http://www.kitchengardenseeds.com/
http://www.lakevalleyseed.com/
http://www.landrethseeds.com/
http://www.livingstonseed.com/index.php
http://www.localharvest.org/store/seeds.jsp
https://www.mainepotatolady.com/productcart/pc/home.asp
http://www.markhamfarm.com/
http://www.mountainroseherbs.com/
http://www.mushroomsfmrc.com/
http://www.mypatriotsupply.com/
http://www.nativeseeds.org/
http://www.naturalgardening.com/shop/index.php3
http://www.naturescrossroads.com/
http://www.neseed.com/
http://www.newhopeseed.com/
https://www.nicholsgardennursery.com/store/
http://www.non-hybrid-seeds.com/
http://www.nybotanics.com/
http://oldpueblocompany.webs.com/
http://www.orchardhouseheirlooms.com/
http://www.organicas/
http://www.potatogarden.com/
http://www.prseeds.ca/
http://qrseeds.com/
http://rareseeds.com/
http://www.reneesgarden.com/
http://www.richfarmgarden.com/
http://www.richters.com/
http://rollinghillsherbs.com/
http://www.ronnigers.com/
http://www.sandhillpreservation.com/
http://www.seeds.ca/
http://www.seedsforthesouth.com/
http://www.seedsnow.com/
http://www.seedsavers.org/
http://www.seedsofchange.com/
http://www.seedstrust.com/joomla/
https://www.superseeds.com/
http://www.southernexposure.com/
http://sowtrueseed.com/
http://www.stclareseeds.com/
http://sustainableseedco.com/
http://www.territorialseed.com/
http://www.thymegarden.com/
http://www.tomatofest.com/
http://www.treesofantiquity.com/
http://www.underwoodgardens.com/
http://www.uprisingorganics.com/
http://www.ufseeds.com/
http://www.victoryseeds.com/
http://www.virtualfarmseedco.com/
http://www.westwindseeds.com/
http://www.wildflowerseed.com/
http://www.wildgardenseed.com/
http://www.wildseedfarms.com/
http://www.woodprairie.com/