Replacement Multimode Fiber Switch 10 base FL

I have an old ABB control network in our plant using masterpiece 200 controllers riding on a serial network called masterbus 300. One of the two multimode fiber ST, 10 base FL switches connecting the controllers to the a windows 2000 server via an optical to electrical convertor failed. So am looking for a replacement switch or advice on what modification I can do.
 
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