It is unfortunate that medals do often get thrown out. It is a reality that people have different focusses and it may be a collector who appreciates them more than a family, or one family member who appreciates them more than the recipient or another family member. But at least you know they were there and have a chance to get the information on him.
First, if he was in WW1 and served overseas he would have got the following:
1914/15 Star, if he served between 5 August 1914 and 31 December 1915. Likely for GSWA and still possible for GEA.
From there he would have automatically qualified for these too:
British War Medal if he entered an active theatre of war, or left the United Kingdom for service overseas, between 5 August 1914 and 11 November 1918, and completed 28 days mobilised service. So if in GSWA or GEA he would have got it too, or if he went to France he would have got it.
Victory Medal if he was in a theatre of war.
Now to find out more about them his unit would help, but you could try a researcher such as Dewald Nel (email@example.com) who may be able to help.
I am not sure if you can search Medal Index Cards for South Africans but if you can then you can find his unit, if you can find his name, and hopefully there aren't too many identical names.