Do you know how I can get past property tax bills.

Check your county tax assessor's website. You can usually plug in the apn and view the past property tax bills. Some lenders will accept a printout of that webpage. Others will have you request a statement from the asessor, but you should also be able to do that from their website.
Good luck!

Call the tax collector or the tax assessor's office.

if you are unable to obtain from the assessor, the title company should be able to provide since most lenders require a tax certification prior to funding

You can an get past property tax bills following ways
• Call at toll free number & gives details
• Contacting the Assessor’s office
• Contacting the Treasurer and Tax Collector
• Email a request for a past bill to the Treasurer &Tax Collector

The local assessor can provide this number easily. For example in Denver County you can get the last 7 statements on their website with the PIN or property address.