I think you want to store the spreadsheet data in Access like this ...
StoreNum SKU Qty
1 1 0
1 2 100
1 3 25
1 1000 1
2 1 5
If that's what you want, keep reading. If it's not what you want, please clarify what you want.
In Access, create a link to the Excel worksheet and name that link ExcelSource.
Then create a SELECT query similar to this:
SELECT
StoreNum,
1 AS SKU,
SKU_1 AS Qty
FROM ExcelSource
UNION ALL
SELECT
StoreNum,
2 AS SKU,
SKU_2 AS Qty
FROM ExcelSource
UNION ALL
SELECT
StoreNum,
3 AS SKU,
SKU_3 AS Qty
FROM ExcelSource
UNION ALL
SELECT
StoreNum,
1000 AS SKU,
SKU_1000 AS Qty
FROM ExcelSource;
If the result set from that SELECT query gives you what you need, convert it to an "append query" to store those data in a table named YourTable. The SQL for that query will be the SELECT SQL preceded by an INSERT INTO ... section:
INSERT INTO YourTable (StoreNum, SKU, Qty)
SELECT
StoreNum,
1 AS SKU,
SKU_1 AS Qty
FROM ExcelSource
UNION ALL
SELECT
StoreNum,
2 AS SKU,
SKU_2 AS Qty
FROM ExcelSource
UNION ALL
SELECT
StoreNum,
3 AS SKU,
SKU_3 AS Qty
FROM ExcelSource
UNION ALL
SELECT
StoreNum,
1000 AS SKU,
SKU_1000 AS Qty
FROM ExcelSource;
If your Excel worksheet includes 1000 SKU columns, create a series of smaller append queries, each of which uses a manageable subset of those 1000 columns.
This could also be done with VBA code rather than a query. I don't want to lead you through that option because I don't even know if I'm on the right track here.