Hi Red,
Yes, you can buy an adaptor, but you don`t really want to, it'd be too limiting.
What you need to play games etc. is a scandoubler - I've got an Eyetech one which plugs into the Amiga's video port, and gives out a signal that the TFT monitor can understand. Check old threads on A.org for discussions about Scandoublers and Flicker Fixers (the latter lets you run more screenmodes which you won`t need).
If you want to do anything serious with your Amiga, though, you need a graphics card.... and for this you either need an Amiga specific graphics card - which will plug straight into the Amiga and talk to your monitor nicely - or else get a PCI backplane. This replaces the Amiga-specific connectors in the Amiga with standard PC-compatible PCI connectors. That doesn`t mean you can run _any_ PC card, but there are a few. I have PCI in my A4000 and it has a standard PC Voodoo 3 in it, runs Workbench on my Iiyama 4636AS 18.1" TFT very nicely. Places like Eyetech (
www.eyetech.co.uk) have a lot of stuff, don`t know about in NZ.
Hope that helps!