Hi Nanni,
Here is a suggestion. I work a lot with crafts and the paints that will adhere to plastic are few and far between.
I purchase a product made by Americana (Deco Art) called Multi Purpose Sealer. It can be purchased at any Michael's store. there are many other products of this type, but for me, this is the best. It can be used as a base, or mixed about half this product to half a craft paint and applied. I also use it as a sealer once paint has set and dried. I tend to use the Folk Art paints made by Plaid, they make some nice golds. You can apply it with a sponge brush or a regular artist type of paint brush. You will probably need two or three coats. I think for this purpose, I would just go with mixing it half and half and apply. Just mix it up in a little palette or in a small dish. It is non-toxic.
Most spray paints that people would normally use, do not adhere well to plastics.
A quicker option, but one you would have to be careful handling, would be to take a gold lustre dust that you would use for cake decorating and drybrush it onto the pillars. Some of it would of course, fall off, but it would be a quick fix.
Hope that helps,
hugs Squirrelly Cakes
Just another suggestion in case the painting doesn't work; maybe try wrapping the columns with gold ribbon; or use both together-paint and ribbon.
how about wrapping the columns with gumpaste or fondant and painting them with gold luster dust mixed with alcohol? Just an idea...
Good Luck!
Debbie 
Did see some on an ebay auction.........but don't remember if they were painted or not.
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