I highly doubt that the encryption - because that’s essentially what is being blocked, the (strong) encryption used by Cloudflare’s (and others’) TLS certs - would be “magically” allowed by purchasing a dedicated certificate. The purchasing issue can be solved by virtually being elsewhere when making the purchase and, quite possibly having to use a currency from a country whose citizens are not currently being punished by any U.S. embargoes / bans / sanctions simply by using an exchange with any E.U. member. Being virtually elsewhere = using a VERY good VPN service or having a friend living outside of Iran doing the entire process for you. However - until you use a TLS cert that’s either a) using a weakened encryption protocol approved for export by the U.S. or b) use an Iranian based SSL company and uploading it to your account (which requires a Business or Enterprise account) the “solution” of using a dedicated cert will, I think, though Cloudflare will need to tell you, not work for you.