If a baby who is a Bechor had his Bris delayed beyond the 31st day - should the Pidyon HaBen be pushed off until the Bris is ready to be done? On one side you do not want to delay a Mitzva in its proper time, on the other hand Bris Milah is the foundation of the Jewish people and without this covenant between Hashem and Klal Yisroel there would be no Mitzva of Pidyon Haben. (sources please)
The Rivevos Ephraim 5:538 explains it is a mistake to think that a bris has to go first.The pidyon can be done before if the baby is still not ready for a bris.
See also 6:441:13 where he brings an actual case where they did the pidyon first.
Firstly you claim that "Bris Milah is the foundation of the Jewish people and without this covenant between Hashem and Klal Yisroel there would be no Mitzva of Pidyon Haben" without providing a source.
Secondly, the Mitzva of Pidyon HaBen is an obligation on the father - who did have a Brit. The firstborn is merely the cause of the Mitzva (and does not even have to be present). Compare it to redeeming a firstborn donkey which is also not part of the Jewish people.
So the usual rules apply: When it's time for a Mitzva then you do it ASAP.
For actual sources you can look up these: