STOVE TOP "Ring Reducer" o algo similar (Mexico City)

Ok...so this is a bit difficult to explain... I think...

I have a gas cooktop but the grates (parrillas) are way to open...meaning that small pots and saucepans are not supported very well or its a delicate balancing act...which can be quite dangerous with boiling water... anyway...I hope you get what I am trying to explain. (PLUS the grates themselves are slick as glass compounding the issue)

Anyway...anyone know where I can buy/find a "ring reducer" as it is called back in the states... its typically a metal disk that attaches or sits on top of the grates of the stovetop....it also helps diffuse the heat (hence it is also called a ring diffuser)...but that really isn't my problem...

I have tried local shops in and around Roma Norte, checked the hardware stores, and even tried HomeDepot, appliance stores...but they don't have the item or know where to look....

** I can explain what I am looking for in Spanish with no problems...but I am not sure what the name of it is in Spanish.

for an idea you can look on amazon - don't necessarily need one just like this - rather something to close the gap of the grates before there is an accident...
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Thanks.