QB Issue Resolution:

Unless you are ready to pay for it all, you should use a PO, then you enter a bill against the PO for only those items that sold.

There is really no shortcut, you could check with the makers of transaction pro importer to see if they can import an excel sheet to a PO (assumes you have that listing in excel).
http://www.baystateconsulting.com/products/01TxnWizard.htm

But if you are running a real consignment shop, you need consignment shop software, it makes life so much easier. Several years ago I demo’d consignment shop software, old comparison but something to start with if you are interested.

http://onsale-apparel.com/Rustler/consignment-shop-software

Resolution for Issue 'What’s the better way to post a extra long bill with thousands of consigned items.' available: Yes (Solved).
Source: Intuit Community forum.

What’s the better way to post a extra long bill with thousands of consigned items.: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for consigned items
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Error Recovery for consigned items [Canada]
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