Is it possible to retrieve current quantity as of a specific date? Thanks.

No as far as I know, the Qty Available is the actual ItemInventory.QuantityOnHand for the stock item. But you could try the valuation report:

sp_report InventoryValuationDetail
show Text, Blank, TxnType, Date, Name, RefNumber, Quantity, CostPrice, QuantityOnHand, AverageCost, ValueOnHand
parameters DateFrom = {d'2010-04-08'}, DateTo = {d'2010-04-08'}

Using the InventoryValuationSummary report gave me the values I needed,  e.g.

sp_report InventoryValuationSummary Show rowdata, QuantityOnHand, valueonhand parameters ItemFilterFullNames = "ASSEMBLY-01", DateTo = {d'2010-04-08'}

The example below put me on the right track but I think it will only return values if a transaction occurred on the select date.

Thanks.

No worries, as always, just choose the report that suits your requirements best:-

sp_report InventoryValuationSummary show Text, Blank, ItemDesc, QuantityOnHand, AverageCost, ValueOnHand, PercentOfTotalValue, UnitPrice, RetailValueOnHand, PercentOfTotalRetail parameters DateMacro = 'ThisMonthToDate'

sp_report InventoryStockStatusByVendor show Text, Blank, ItemDesc, ReorderPoint, QuantityOnHand, QuantityOnSalesOrder, QuantityAvailable, SuggestedReorder, QuantityOnOrder, EarliestReceiptDate, SalesPerWeek parameters DateMacro = 'ThisMonthToDate'

sp_report InventoryStockStatusByItem show Text, Blank, ItemDesc, ItemVendor, ReorderPoint, QuantityOnHand, QuantityOnSalesOrder, QuantityAvailable, SuggestedReorder, QuantityOnOrder, EarliestReceiptDate, SalesPerWeek parameters DateMacro = 'ThisMonthToDate'

See: How do I use the QuickBooks Reporting Engine with QODBC? I've heard something about sp_report ? for more.