Yes I produced my own scoby from a drink purchased from the people at the seminar. Online it said it'd take 4-6 weeks to grow but I seriously had a fully developed thick scoby in a week maybe less.
I hear you can do this from a regular kombucha as well such as GT's synergy brand or whatever. Just have to get an unflavored original not a flavored one. The tea has been at least partially compromised if its been flavored. This is because when you flavor a batch of kombucha you brew as normal but when its finished mix in a separately prepared tea of choice flavor at around 25% flavor tea to 75% kombucha. Idk for sure but I'd figure some of the flavor additives will introduce something that may kill the beneficials in the kombucha.
I've been drinking kombucha since I was a baby - so I second what MadPlanter said - you never need to buy a scoby - it's all a money making ploy.
The secret is to buy alive kombucha drink - some of them are pasterized and thus are dead - they taste like kombucha but they have 0 kombucha benefits since the culture is dead and you are drinking a sugar soda-like drink instead.
I have never had a problem with flavored kombucha to use as a starter. I usually buy a few bottles to speed the process up, add strong black tea and lots of sugar and the scoby appears usually overnight or the next day when left at the room temperature under the cheeze cloth (to avoid fruit flies laying eggs in your scoby).
GT brand is a proven live kombucha, at least it formed a scoby every time I tried.
If you are using a different brand and the scoby doesn't form within a few days - don't ever buy that brand again - most likely they sold you a pasterized dead kombucha.
Finally, you can store your culture in the fridge easily for 6 months or longer, just put a nice concentrated tea and sugar in it before you store it - it hybernates nicely but it does consume some of the ingredients over time. I usually don't like drinking kombucha in winter, so I park it till spring time.