Any help would be greatly appreciated regarding this time sensitive matter!!

Ask if it can be done on line..   

Although I have already read about the laws related to security deposit matter in CA Civil Code Section 1950.5, I would like the property owners with similar experiences to me consider my situation and advise me regarding the following items1- How to calculate their security deposit and provide an itemized list, while I do not have any invoice in my hands. 2- As my tenants have not left any forwarding address, shall I contact and ask her the new address for sending the itemized list?

On those few occasions when someone from the other party contacted me directly instead of going through her, I let her know immediately so she could deal with the matter. 

This works to your benefit as well.A majority of people I speak to want to get a non-exclusive agreement with me and it is very much a matter of if you can't commit to me, why would I commit to you? 

I have made many many attempts to collect and even suggested that setting up and online pay would make things easier (I did that) and they still haven’t paid.

It's compounding, every dollar matters especially positive cash flow.

Does anyone host or know of meetups that may not be posted online or advertised very heavily?

First the type of real estate doesn't matter as long as it is used for investment. 

Does it matter?