I would ask at your local shops to see if they can order sterbai for you. I've seen them even at petco/smart chains in the last few years, Not always, but worth asking about. It may depend on how many you want too, they may have to get 12 or something.
I would order from Wet Spot (expensive shipping! I drove mine home on vacation), maybe Aquabid but I have little experience getting mail order fish. Live Aquaria has some pretty bad to ok (ish) reviews lately. I used to live near That Fish Place with mixed fish quality but that was a very long time ago. Do they even still sell fish by mail anymore?
There are some other places I've never heard of more than a couple times here on AC & maybe another board or 2. I may have the names wrong, Aquahuna, Angels Plus, ?something guppies?
Sterbai are not so unusual that if you have a local-ish club someone might breed them. Ask on their board. There are likely going to be spring meets/auctions coming up soon, might be worth a drive for a fun day out...
Depending on where you live March might still be a bit chilly for shipping fish even with heat packs bad things might happen. Where I live we worry more about heat, so keep that in mind. Where fish are from & where they're going & the form of shipping you'll pay for...might be more than a tank full of gas if you live near a big city...Call ahead to some stores & maybe have a fun road trip with a new restaurant too?
In a general way, where do you live? There are many clubs & shops.
Oh, & just so you know there are albino sterbai now too. They have orange pectoral spines to differentiate them from other albinos. I don't know if those are acceptable to you, I tend to prefer "natural" fish.