Hi John,
Cape Gooseberries are still around but perhaps a bit scarcer now than they
were. NZ had a go at commercially producing them and they were available for
a while in specialist fruit shops (this is about ten years ago now). They
bear very little similarity to the European gooseberry.
The plants tend to grow in dry, neglected areas and were common in WA in my
youth...they were essentially a "kids" fruit... like loquats although I can
remember quite good jams being made from them. The fruit is sweet and tart,
yellow/orange when ripe and about the size of a marble. The fruit is encased
in a "lantern" which dries out to a straw colour after which it falls to the
ground. A good producing plant might have anything up to 30 of these ripe
fruits lying in their dry lanterns on the ground under the plant. If the
plant grows in good soil, it will tend to put on a lot of vegetative growth
and produce little fruit...perhaps like the ones you came across. I managed
to pick up some ripe berries late last year from a friends place in northern
NSW but have not had success in getting the plants to grow from seed yet. I
have seen them growing in Qld and the NT as well as NSW and WA so they are
pretty wide spread but, as I said, do not seem to be as prolific now as they
once were.
I don't recall ever seeing the plant for sale in a nursery.
Hope this helps (they are not some form of horticultural urban myth)

Irvin Savage