Sometimes you can't get records from GRO because they only have records for certain years, so perhaps just check the dates (in years) you are looking for, with the years available on the GRO website.
See if there is anything in relation to Norwood orphanage which took in many Jewish children.
The 2 main groups (other than for Sephardi burials) are the Western Charitable Foundation Burial Society or United Synagogues, so check their websites.But then to find the plot, you need to know the cemetery. However, when I have called them, I have found them to be very helpful.
I hope some of this helps,
Terry Ashton, Australia