Though the noob is looking for a 1-3/4" tire. Unless that is a mistake. That's probably a very rare 27" tire if they ever made on that size.
All I can say for that is they need to look at their old tire. Google to see if the manufacturer is still making 27" tires in that size and then find out where to buy them. Many mfr's have a dealer locator or where to buy on their site if they don't do online sales themselves.
And the noob should also double check the old tire for the ISO or ETRTO size that probably is embossed or stamped on the tire to double check this isn't some kind of other than 27" tire that just says 27" on it. Maybe a 27.5 x 1.75 tire which is for a 584mm bsd rim, not the 27" tires 630 bsd rim.
Oh....
Johntcl welcome to BF ! We sometimes are a little blunt and brutal here. Just read everything with a smile and don't let us get under your skin. We mean well in spite of ourselves.