There's a black market for Black Caviar.

Racegoers at Randwick were happily prepared to pay $80 for a cap stamped with the champion mare's pink and black polka dot signature colours.

Hours after merchandise stalls sold out of Black Caviar gear ahead of her hotly-anticipated win in the TJ Smith Stakes at Randwick on Saturday, some enterprising racegoers were spruiking the gear at heavily-inflated prices.

By mid-afternoon, racegoers had snapped up 500 caps, 1400 stubbie holders, 40 cufflink sets, 50 plush ponies - not to mention hundreds of ties, key rings, keychains and magnets - within hours of the stall's opening.

And they can't get enough, according to stallholder Ashlee Graham.

"In such a small little area, I haven't seen queues so big," she told AAP.

"We were expecting it to be very consistent, but not as busy. At one point the queue was up to the gate.

"Everyone wants just a little something, like stickers or key rings, so they think they've got something of her."

Sue Riddington from Sydney said she was celebrating what would be an historic day by buying a sticker to "pop on the back of the car".

"It's a really special day for us, so to get something like this and have it for keepsakes, we can have something for 25 years and remember this day," she said.

"We used to hear dad talk about Kingston Town and he used to take us to the races, and today we are doing the same."

Karen Irwin said while she wished she could own a part of Black Caviar, a cap would be the next best thing.

"It's all part of history, isn't it? So it's always nice to have a little memory from today."

The lucky people who did get their souvenirs were not disappointed, with the great mare thrilling the crowd with her 25th win and her 15th at Group One level, an Australasian record.