As Dobby suggests contact the farm, I recently made an enquiry and this is the information given.
Some of the land is being used by the Rice Lane City Farm which is a Community Project and one of the volunteers accepts specific requests for research for specific graves.
Firstly there is no official plan for the cemetery, however they do hold an informal plan, there are a number of avenues noted alphabetically and they believe they have approximately a 50% success rate.
It is recommended that you make contact by email -
ricelanecityfarm@hotmail.co.uk and a Grave Reference is absolutely essential,
not just a name and date of death. They will need a minimum of a couple of weeks to try to find any information for you, it's not a straightforward task for them, so don't just email and say you are visiting Liverpool tomorrow.
As they are a Community Project donations for any research undertaken are suggested and are always welcome.