Is there an adapter to fit the Sigma 70-300mm 1:4-5.6 APO Macro super lens to the body of a Sony a200
That lens is available from Sigma with a Sony mount, so there's no need for an adapter if you haven't yet bought the lens -- just buy the Sony version.
If you already have the lens for some other mount, see Can I use lens brand X on interchangeable lens camera brand Y? for information about which mounts can be adapted to which others and what drawbacks might be involved.
It looks like the a200 has a Sony/Konica/Minolta A-mount, which has flange focal distance (FFD) of 44.5mm. So, if you have the Sigma 70-300mm lens with a Canon EF mount, you won't be able to adapt it because the Sony's 44.5mm FFD is greater than the 44.0mm FFD that EF lenses require. On the other hand, the Nikon F-mount's FFD is 46.5mm, so if you have the Sigma lens built for Nikon, you may be able to use that lens on your a200 with an adapter like this one.