RAC HP021 - missing screw to affix detergent holder?

My Father in law bought an RAC HP021 pressure washer from Woolworths.

He has only just gone to use it and found the 3 screws missing that affix the detergent holder

I have tried contacting the manufacturer and spares companies but no-one has helped. All I need are the three screws replaced or if someone can tell me what size, type etc of screw we can substitute !!

Please please help !!! Thank you so much