The other day I came across this line in a game:
しかしそれ以外は誰とも出会わず、そして 歩けど歩けど 代わり映えしない通路と部屋ばかり。
I guessed that 歩けど meant 歩いても from the context, but I had never seen a verb conjugated like that before. Is it something from a dialect, or perhaps classical Japanese?
The conjunctive particles ど and ども are Classical Japanese contradictory conjunctions, like the English but and although. Although they aren't used as much anymore, you surely know them from the modern けれど(も), and you probably know them from いえども and されど as well.
They attached to the 已然形 (realis stem), which in modern Japanese has been reanalyzed as the 仮定形 (hypothetical stem). In this case, that stem is 歩け, so you get 歩けど.
Here, the 〜ど〜ど pattern has the verb redoubled for emphasis:
歩けど歩けど
Since it's literary, we could try to give it a literary sounding translation:
歩けど歩けど、岩しか見えなかった。
Walk and walk as I might, I could see only rocks.
Hopefully you can see the meaning from this simplified example.
It comes from Classical Japanese but it is used in Modern Japanese much more often than you appear to think.
「ど」 is a contrastive, conjunctive particle. 「[歩]{ある}けど」 means the same thing as 「歩くけれども」 and 「歩くが、しかし」.
You speak of the conjugation but the ど is not part of the conjugation. 歩け is the [已然形]{いぜんけい} of the verb 歩く.
