DIY Yard Gum Drops???

Just wait until that store opens again after the holidays, then order them.
Their cost might be just as much, as making it yourself and buying all the supplies for it etc. Might as well wait and see how much they sell it for....or call them on that number they list on their site.

Or use "Floam" to get that desired effect of the "gumdrop." Its a kids "toy" thing. But if you get it wet, it is not permanent.
http://www.does-the-product-work.com/floam/

Here is a link from this same store per your link, in E-bay:
http://www.ebay.com/itm/CANDYLAND-WONKA-CHRISTMAS-BIRTHDA...
They describe how they make it but obviously do not say their "secret" for making it exactly.

http://www.ebay.com/sch/maryschristmas/m.html?_nkw=&_...

That's a tough shape. A styrofoam cup would be smaller and you would need to texturize it. Maybe with that spray insulation? Great stuff, I think it's called? Use gloves! May be with a clay pot water catching bottom glued to the cup to give it weight for outdoor use.
Could do air dry clay over the top of the cup instead of the insulation stuff, just to round the shape out.
I love theme parties.

Maybe buckets for forms. fill with spray foam? The buckets would need to be lined.. but not sure what will not stick to spray foam..

Then you sculpt them to look like gum drops.

Then you can spray paint them then spray frost them?