Welcome!
While several people are recommending places to buy from, I would urge you to do extensive research before rushing out to buy.
The fact that you said your "dose" is 50 units, tells me you don't understand enough, yet. I see you have the mg after being asked, but it seems like you might need to do more research first.
Where you buy from depends on your trust level. Some people have no issues using a product based on a test result the vendor showed them. Others want to send a vial or 3 from what they bought to make sure what they received matches the test the vendor showed them. Some want sterility testing done, and some will inject anything a stranger hands them in a dark alley, lol
I suggest you do A LOT of reading, decide which level makes you comfortable, then go from there.
Just asking for a vendor, or recommending a vendor that fits your style to someone you don't know, is a bit reckless, imo.
This forum encourages everyone to do their own research and determine safety for themselves. We are here to answer questions and guide you.
Feel free to ask any questions, search the forum, jump into conversations, or create a new thread for a specific topic.
There are many other places to pull research from too, and we can direct you to those.
This is a grey market where the products come from China, not a US pharmacy. Not everyone is comfortable buying injectable substances from a foreign company. And this market isn't Amazon, so you can't just submit a return and drop it off at the UPS store. Generally, once you buy something, it's yours and your money won't be refunded unless you spend $350 for a test, from a certain company, and the test shows a problem.
Make sure you know what you are buying and getting into! Make sure you know what guarantees are/are not in place. Make sure you are comfortable receiving vials that don't have labels on them and aren't linked to a test, if you choose that option. Make sure you know how to reconstitute lyophilized product, what tools you need, and how to calculate doses... Before you buy!