It will be released in distribution.
20-xxxx codes are distribution pieces, while BT-xxx are only available directly through IWM. Other variations you might see are CE-xxx (con-exclusive), or LTD-xxx (limited edition), which may also be carried in IWM's online store while supplies last. For example, the 3150 Davion lance likely had a CE-xxx sku, while its constituent minis sold individually will have their own BT-xxx skus.