SELECT accounts.a_id, accounts.StoreName , products.UPC , products.ProdName
FROM accounts
LEFT OUTER JOIN products_accounts ON accounts.a_id = products_accounts.a_fk
LEFT OUTER JOIN products ON products_accounts.p_fk = products.p_id
and, if there is potential for repeated account-product pairs then maybe:
SELECT accounts.a_id, accounts.StoreName , products.UPC , products.ProdName
FROM accounts
LEFT OUTER JOIN (
SELECT DISTINCT
products_accounts.a_fk, products_accounts.p_fk
FROM products_accounts
) ap ON accounts.a_id = ap.a_fk
LEFT OUTER JOIN products ON ap.p_fk = products.p_id
FROM accounts t1
INNER JOIN products_accounts t2
ON t1.a_id = t2.a_fk
LEFT JOIN products t3
ON t2.p_fk = t3.p_id
unless I am missing something about your tables that should return what you want.