A scuba pro 450 is a 6306 diver with a branded dial so an authentic one will be hard to find and probably pricey, to give you an example a very nice normal dial 6306 was advertised on here for £750 I think recently. Good write up from a member here on the scuba pros https://www.google.co.uk/amp/s/thewa...bapro-450/amp/
Tons of aftermarket scuba pros dials fitted to the more common 6309 on eBay buy then you’re back to the problem of not being a proper seiko really!
Other alternatives from seiko..? There’s loads maybe the reissue 6309 is a place to start?