When I took Sudafed before being on Adderall XR, I didn't notice any improved focus.
ADHD treatment definitely merits going through official channels, meaning a licensed prescriber and a real pharmacy. The most effective treatments are usually schedule two controlled substances. That means the drugs are very illegal when obtained through illicit channels. The pills are not super costly. A 90 day supply of the maximum strength pills should cost you about $35 using a GoodRx coupon. Whether you believe that you need a medical doctor for diagnosis and treatment -- and I think you do -- the legal difficulties mean you should stay away from schedule two controlled substances not dispensed to you by a pharmacy.
About six months ago, when I went to see my psychiatrist, the receptionist demanded that I pee in a cup. I didn't understand why; I obviously was going to test positive for amphetamines. (No, it's not like meth. People don't typically get addicted. Doctors who treat ADHD usually believe the side effects are less than the non-stimulant medications.) I did as instructed. When I saw the doctor, I asked him why. He said the California DEA forces him to conduct such tests. He said the purpose was to make sure that I wasn't selling the Adderall to others. That thought had never occurred to me - I had become so much better at my job as a lawyer and just life in general by using Adderall that there is no way I'd stop using unless there is was major medical thing requiring that I stop. I do in fact have ADHD and was diagnosed long before there was Adderall. My understanding is that while some folks use Adderall who don't have ADHD and find that it improves focus, that there are many more difficulties experienced by those who use it if they don't have ADHD. Since I do have ADHD, I have no personal knowledge of what it's like to use it for a person who doesn't have ADHD.