Many branded metal 7" reels are highly collectible these days and hence, expensive. They were mostly all an optional extra. The early Akai reels are some of the most desirable - they are the ones with AKAI cut out of the metal. They're a lovely reel to use too because threading is so easy. It's my reel of choice on all my Akai decks as take-up for 7" reels. These are pricey reels. Later Akai reels (three slot or flower) are much more common but still in demand. You should be able to find average examples of these for much less than the early ones. The other really desirable 7" reel is the Sony R-7MB. Most common was silver alloy, then black, and then the colours - red, blue, green, gold. It's a beautifully made reel but not as easy to thread as the early Akai - then again, nothing is! These reels are quite pricey secondhand and even more for the coloured ones.
These days your best bet to find any metal 7" reel is eBay. Just be patient and do go too crazy. A good option is to buy a small collection of reels that may contain the one you want. Then sell on any you don't want.