My sound system blew a speaker, where do I find a replacement speaker?

I need a 4 inch - 8 ohm speaker the manufacture says is discontinued. It is a perfectly good sound system and i do not want to trash it for one blown speaker. I tried looking all over the Internet for a suitable replacement speaker. Every web site has junk search engines that just bring up all kinds of suggestions for things they want to sell rather than finding the speaker I need. A 4 ohm auto speaker will not work because I am told it will draw current faster and heat up the amplifier of a home sound system thus causing damage to the amplifier and the rest of the system. I guess there are no adapters to make a 4 ohm speaker work in place of an 8 ohm speaker or are there any? I may have to build a new speaker cabinet that will hold a set of 5 1/4 inch - 8 ohm speakers. I would like to know where I can find replacement speakers for a home sound system. Radio Shack does not carry them. They like all the rest try to sell something I do not need that will not work. I need the 4 inch -8 ohm speaker only. Where can I find one?