From the looks, the ODI Viking 1911 used a standard rear dovetail and a ramp front sight.
If this is how your's is set up, any 1911 rear sight that will fit a standard slide's rear dovetail will work.
Brownell's sell many rear sights for the 1911 series, from drop in to types that need the slide to be machined to fit.
Most any competent pistolsmith should be ale to fit a rear sight, and if necessary a different front.
Depending on how yours is set up, all you may need is to install your choice of rear sight.