Just to clarify, as you're in America I assume you mean Celastrus scandens not Solanum dulcamara, which is bittersweet in the UK.

There are three plants which may be commonly known as bittersweet in the USA - see the link below for an extensive explanation, but basically, they're Celastrus orbiculatus, Celastrus scandens and Solanum dulcamara. Best to decide which one you're actually looking for using the botanical, Latin name when you look or ask to make sure that's what you're getting. I find it hard to conceive that you're looking for seeds or plants of Solanum dulcamara, given its poisonous and invasive, so its probably one or other of the Celastrus you're looking for. However, it would be best to stick to Celastrus scandens, since C. orbiculatus, whilst somewhat more attractive, is considered a highly invasive, destructive vine, with a root system that's difficult to kill once it's taken hold. Celastrus scandens does not produce edible berries, but if eaten, other than making you have a rather bad stomach upset, they do not kill.

Once you've decided which plant you mean, further advice as to how to grow could be given.

https://www.thespruce.com/oriental-bittersweet-vines-2130878

Is it possible to buy male and female seeds? All the seeds will come from the female plants so surely there's no way of knowing?

Celastrus is dioecious--that is, the male and female flowers form on separate plants--but to the best of my knowledge, there is no non-destructive way to determine which seed will be which gender. It sounds like a scam, Cynthia.

Thanks to all for you comments. I'm wanting to plant celastrus scandens. I use to be able to get from friend's yard but they have moved. I decorate with in the Fall.

the seeds will not be gender specific by looking at them, as it is determined by genes on the DNA that you cant see.

Yep, the only way to tell would be to take a DNA sample from the embryo in the seed, which would likely keep it from ever sprouting.