Like you I loved the old keyboards with the "buckling" mechanical springs that had such a nice crisp touch and made that wonderful "click" when the character was typed. Many believe this type of keyboard reached its zenith in the famous IBM Model M keyboard. So much so that a
used 122 key Model M keyboard can easily bring $90 to $120. Others give the edge to the classic Mac keyboard and you can't even find one of them on the used market.
You aren't going to find a new Apple computer that recognizes the keyboard power key, much less a new keyboard that has one, so it is a good thing you can live without it.
Matias used to sell Mac compatible buckling spring keyboards but apparently all those models have been discontinued in favor of keyboards with the ubiquitous and less expensive dome switches.
Das Keyboard has the buckling spring switches, is available with Mac keycaps and with the Mac keycaps runs $144 USD. I could not tell from the pictures on their website, but I suspect since they are more Windows centric the shift key issue would still be present.
Unicomp keyboards cost around half that amount but make no pretension of Mac compatibility which would leave the shift key issue to deal with. I embarked on a similar search a few years ago and seriously considered the Das Keyboard models. However, since I have a tendency toward Carpal Tunnel I ended up choosing the
Goldtouch adjustable keyboard for Mac at $129. It does not have the buckling spring keys but the dome switches they use have a very similar sound and touch although not quite as crisp. It took some getting used to the split keyboard design, but I have become a lot faster and better typist than I ever was on a straight keyboard. NOTE: the Goldtouch keypad is an extra device at extra cost.
Good keyboards are not cheap.
