You have several ways to find out the 'real' owner of the property. For example, you can look at the tax records and see if they show a valid street address.
However, in the event that you can only find a P.O. Box (or even a PMB), the service of legal notice is a permissable cause and the server can file a form (PS Form 1093 for US Postal offices, Form 1583 for Private Mail Boxes) to find the 'real' address of the boxholder. This is covered under 39 CFR 265.6 (Code for Federal Regulations, part 265.6) which can be viewed at:
http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=39&PART=265&SECTION=6&YEAR=2000&TYPE=TEXT
And one more thing to consider. If you provided a new address when you moved, the landlord is REQUIRED by statute to provide an accounting of your deposit account and refund any available funds. Here are some Texas Statutes that might apply to your case (all are in the Texas Property code, Chapter 92):
"§ 92.103. Obligation to Refund
(a) Except as provided by Section 92.107, the landlord shall refund a security deposit to the tenant on or before the 30th day after the date the tenant surrenders the premises.
(b) A requirement that a tenant give advance notice of surrender as a condition for refunding the security deposit is effective only if the requirement is
underlined or is printed in conspicuous bold print in the lease."
"§ 92.104. Retention of Security Deposit; Accounting
(a) Before returning a security deposit, the landlord may deduct from the deposit damages and charges for which the tenant is legally liable under the lease or as a result of breaching the lease.
(b) The landlord may not retain any portion of a security deposit to cover normal wear and tear.
(c) If the landlord retains all or part of a security deposit under this section, the landlord shall give to the tenant the balance of the security deposit, if any, together with a written description and itemized list of all deductions. The landlord is not required to give the tenant a description and itemized list of deductions if:
(1) the tenant owes rent when he surrenders possession of the premises; and
(2) there is no controversy concerning the amount of rent owed.
"§ 92.107. Tenant's Forwarding Address
(a) The landlord is not obligated to return a tenant's security deposit or give the tenant a written description of damages and charges until the tenant gives the landlord a written statement of the tenant's forwarding address for the purpose of refunding the security deposit.
(b) The tenant does not forfeit the right to a refund of the security deposit or the right to receive a description of damages and charges merely for failing to give a forwarding address to the landlord.
And this one is the MOST IMPORTANT:
"§ 92.109. Liability of Landlord
(a) A landlord who in bad faith retains a security deposit in violation of this subchapter is liable for an amount equal to the sum of $100, three times the portion of the deposit wrongfully withheld, and the tenant's reasonable attorney's fees in a suit to recover the deposit.
(b) A landlord who in bad faith does not provide a written description and itemized list of damages and charges in violation of this subchapter:
(1) forfeits the right to withhold any portion of the security deposit or to bring suit against the tenant for damages to the premises; and
(2) is liable for the tenant's reasonable attorney's fees in a suit to recover the deposit.
(c) In an action brought by a tenant under this subchapter, the landlord has the burden of proving that the retention of any portion of the security deposit was reasonable.
(d) A landlord who fails either to return a security deposit or to provide a written description and itemization of deductions on or before the 30th day after the date the tenant surrenders possession is presumed to have acted in bad faith.
All of these can be found at:
http://www.capitol.state.tx.us/statutes/py/py009200toc.html
Finally, if you will email me privately with information on the property (address, etc) at the address shown in my signature below, I might be able to help you.