Charles Sumner and the Coming of the Civil War and
Rebels at the Gate are additionally 1.39 pre-coupon at Kobo (Canada), but don't seem to show up for the US when I do the search from Ye Olde VPN IP Proxy.
The History Buff's Guide, on the other hand, is geo-restricted and unavailable to Canadians.
Sourcebooks' eBooks specials listing page says that they're all $1.50 for the 150th anniversary of the US Civil War.
So possibly the last remaining available one (
Stealing Secrets) will drop at Kobo eventually. It looks the most interesting of the lot.