or FontSquirrel : Well-known repositories for free and legal fonts (always check the license). Adobe Fonts : Included with Creative Cloud subscriptions.
It looks like you're looking for a download link related to — but I couldn’t find any legitimate or official source for a font with exactly that name. stdx603fontdownload link
Get the stdx603 Font – Download Link Inside or FontSquirrel : Well-known repositories for free and
While STDX603 isn't as common as Arial or Times New Roman, it’s a workhorse for technical documentation. If you can't find a direct download, look for or check your software's original installation media. stdx603fontdownload link