It's a prescription only medicine, sorry! Having said that, you might be able to get it off the internet but be careful. It may SAY Liverpool cream but could be battery acid! Or nappy cream!
The vet send pics of the sarcoid to Derek Knottenbelt at Liverpool Vet College and he then prescribes the appropriate cream. Sometimes it is smeared on, others injected, so you can't buy it yourself, it's too strong.
Ask your vet.
it is highly cytotoxic and not even able to be handled by the general public, let alone bought. you need to get your vet to send pics to DK at Liverpool who then makes up the right strength of cream and sends it to your vet who has to come out each time and apply it - normally every other day for 10days or similar.