Where can you buy fossilized flowers (online)?

Try The Smithsonian National Museum of Natural History's Botany Department. The website is:

http://www.nmnh.si.edu/botany/

and there is a contact page. I bet a researcher there would be able to provide you with that information including what you could expect to pay for it.

Fossil flowers are about as rare as chicken's teeth and I doubt that if you do find one for sale the price will be within the range of your pocket. The nearest you are likely to get are fossil leaves which are quite common in some deposits. Eurypterida are also not in great supply but another attractive alternative is a nice trilobite specimen. These are easy to obtain on-line, just do a Google search on trilobites for sale to see the choice. An ammonite which has been cut in two and polished showing the internal chambers of the shell can make a beautiful item even without the extra excitement of knowing its past. Good luck with your search, I think you have had a great idea for a gift.

I also discovered the cost of those types of specimins! So instead, I went with resin casts. Archaeopterix in particular. Now that is a 1 of a kind fossil that could never be purchased. It is also extremely important historically as the 1st physical connection between birds and dinosaurs. The cast is realistic you would not know it was fake without a magnifying glass. It is also a great piece of art about 2'x1' in size. I really enjoy it even though I know it is not real.

Huge shark teeth, skulls and other items are now available in resin casts. The originals are usually museum pieces so the casts are very detailed - you can even feel the serrations on the shark teeth!

I got mine from a local dealer, but do a web search or check on Ebay for resin fossil casts or similar.

That's an interesting gift. I guess you would never have to worry about watering it!

I don't know where you get fossilized flowers but you can try

flowershopdeals.com for the eurypterid specimen type. It list some of the major florist online.