Unforunately there are no shops that I know of in the UK or Ireland that sell "vintage" tamagotchis. If there were, I would probably already have visited them
Most shops only sell the latest version (V5) and any stock they still have of the previous versions such as V4.5 or V4.
Very occasionally, you might find one in a second hand toy shop - but these are usually the more recent versions - V1-V4 for example.
The same applies to things like school jumble sales or car boot sales / yard sales. Sometimes you find an old version. But I have to be honest, I've never seen anything older than a V1 in these kinds of places.
In order to buy a Mothra, Forestgotchi, Angelgotchi, etc. you have to use the internet.
They are often sold on ebay and sometimes by members of TamaTalk through our tbay forum - although most of the members (sensibly) use ebay to sell their old tamas to cut down the risk of being scammed. It's no fun if you send someone a postal order and they never send you the tama :furawatchi:
Otherwise, you can use trustworthy websites that sell tamas such as:
https://www.tamenagerie.com