After a while of searching, I think I found them...
This link will give the best explaination:
http://africa.worldofcoins.eu/af-uga2.htm
Wiki says the last coins from the First shilling were issued in 1986; however, if the unissued coins from the above link are the same as the ones in question, the coins could have been struck in 1986, yet dated 1987 (since they were supposed to be released in 1987).
And the compositions of the 1 Shilling and 50 Cent pieces do match--they were nickel-plated steel.
So... maybe those ones?
(And I did send some requests to add these missing coins.

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