Earthly Delights - both fresh & dried exotic mushrooms & other wonderful things. I've ordered from them before & the quality & customer service have both been terrific.
Dean & Deluca - well-known purveyor of nearly everything under the sun. I've ordered from them not only for myself, but have sent gifts from them as well - all with excellent feedback.
Penzey's Spices - again, have purchased for both myself & as gifts for others. Terrific in every way.
There are lots of others I buy from online. If you do a search for whatever ingredient you're looking for, you're bound to come up with dozens of online sources, no matter how exotic what you're looking for is.