I would be very suspicious of any catalog listing Hoya gigas as you are likely to end up with some other Eriostemma. The only time I have seen a photo was on the Paradise Forest site and then it has not been verified. The photo does resemble what you described with a very dark flower colour along with that Stapeliaesque flower shape. The floral scent being like that of a Stapelia is very interesting, not sure if I can think of another carrion scented Hoya or Eriostemma.

Mike

Here is a link that might be useful: Paradise Forest

Hi RFG,
Your best bet might be to contact the Swedes. They keep up with all the newest Hoya's and are close friends with a lot of the new age trekkers who go out on collecting trips. A lot of times the Swedes get/have Hoyas we in the USA haven't heard of yet or seen for sale. The Swedes have amazing collections and are fantastic growers! They also if a true collector are sticklers for correct names.
The flower size is amazing from a picture I saw on the net and would be a sight to behold in person!,,,Debbie

David Liddle did have a new eriostemma he claimed to be the real gigas. Of course this is like finding the rare sasquatch or abomidable snowman. Original botanists described this most unique hoya with flowers large like saucers.
The one listed in most catalogs is not the true gigas, but at the time I threw the towel in, there have been two collections which did possess a plant they claim to be the real deal. I was just curious if anyone has ever seen or touched this plant.

Not that anyone would want this in their home, but it does pose special potentials for breeding with it.

https://www.facebook.com/uppsalalinneanska/photos/nu-blommar-hoya-gigas-i-tropiska-v%C3%A4xthuset-f%C3%B6rmodligen-%C3%A4r-det-f%C3%B6rsta-g%C3%A5ngen-denn/10152347727606389/

Translation of the text on the above FB link

2014-10-23 Hoya gigas blooming in the Tropical Greenhouse, Uppsala, Sweden

Hoya gigas is now blooming in the Tropical Greenhouse. This is probably the first time this unusual porcelain flower has ever bloomed in Europe. It is wild in New Guinea, where it is threatened by deforestation. The conservation project "Paradise Forest" works to preserve species within the porcelain flower genus.