The たらなら construction seems to be something that is in use. Examples like 居たらなら, 食べたらなら and others are easily found on the web, in fairly copious numbers, as well as だったらなら, and even だったらならば.
だったらなら is mentioned in this this thesis paper about guiding Chinese students of Japanese in the use of conditionals. In a section that presents the finding that 26.79% native speaker subjects in its study found だったら a bit unnatural compared to だったのなら, this sentence appears:
The author seems to take だったらなら not only for granted, but as something a bit more natural than だったら alone.
Conjecture: in rapid speech (早口), たらなら and たのなら can sound almost the same: the の or ら just get a quick tongue flap. Also, the "o" sound in の is surrounded by two "a" morae, so it pulls higher toward "a". It seems that the difference between the two readily succumbs as a casualty when people are engaging in 早口.
Tongue twister time: さようなら、「たのなら」、これから「たらなら」。（＾＾）