1/72 omaha beach

Italeri has a d-day dio set, as a part of their wargame. They might have the models in separate sets.

http://www.italeri.com/product.aspx?item=6700S

Great Models has that DML/Dragon LCM Diorama kit listed for $14.20.
The base is 13" long by 9" wide.

Good price for what you get. Get 2 (that will give you 2 LCMs, with 6 crew figures and 24 infantry figures from the 29th Div. for Normandy. Place them side by side. Then you just have to, if you want. expand the beach area. Get the barbed wire (see my answer to your thread in the Diorama forum) from Accurate Armour.

Also search around on Great Models. They also have "barricades" that you can put on the beach, etc...

James

And this
http://www.missing-lynx.com/reviews/small/dmllcm3_csewell.html
http://www.dragonmodelsltd.com/catalog/dml/new/7257/7257-p2.jpg

Well,I think those are best suited for your diorama...
http://www.plasticsoldierreview.com/Features/DRAG7257.html

Lots of figs available for this. Best bet is 20mm wargame figures.
http://www.wargamesdirectory.com/html/periods/view.asp?ID=59
scroll down to the figures section here and then check out the sites with 20mm figs.
Good luck on your project.