It’s just a Unicode character, so you can get it just like any other (including emoji):

• use a phone/tablet virtual keyboard that lets you pick it directly, or a utility like “character map”
• type it using the Unicode code point (U+221E in this case) and whatever modifier key sequence is necessary for your OS
• search the web for “[symbol name] Unicode” and copy/paste

Usually the 3^rd way is easiest, for arbitrary unusual characters like this one.