Who to contact for a PIP application form ?

Hi @lottery45 and welcome to the Community.  It is nice to meet you and thank you for your enquiry.  I believe that it is quicker to apply for PIP by phoning the DWP on 0800 917 2222, but if you would prefer to apply for a PIP application form then you can write to them at -

Personal Independence Payment New Claims
Post Handling Site B
Wolverhampton
WV99 1AH

Please find some information regarding PIP below which I hope you will find useful - 

https://www.gov.uk/pip/how-to-claim

SCOPE also has some useful information on PIP below -

https://www.scope.org.uk/advice-and-support/personal-independence-payment-pip/

I hope this helps, but please let us know if you require any further help or support and good luck with your PIP claim.  All the best.  :-)