Am a member of a Residents Association but thankfully don't have the problem you're experiencing. If it's a service charge set out first day when you bought the house/apartment then all should legally be paying. But if it's a voluntary type thing that's different. We don't have a communal green (unfortunately) but has your park been taken in charge by the council? If so then they have guys who come and cut the grass. On an annual basis the council tends to send out notice of the availability in your area of say a communal skip in which to get rid of bigger items that won't fit in your bin though they do stipulate the materials that can and can't be put in it. The council also usually annually alert Residents Associations of paint tin pick ups - usually sponsored by one of the pharma companies.
Alternatively, you could apply to one of your local councillors for a donation from his Ward Fund to go towards the financing of the clean up.
As for Landlords who make 1500 pm on rent but won't contribute when asked, one can only presume you've contact details for them. That being the case you can alert them to the fact that if they don't contribute their fair share Revenue might be alerted to their rather hefty revenue stream. Just a suggestion like
