Clarification: HDPE (high density polyethylene) is NOT a good choice for developer, because of high permeability to air oxygen. Soda bottles are likely PET (polyethylene teraphtalate) a vastly better oxygen barrier. Hopefully, where you live, bottles bear a code indicating (for recycling) what type of plastic; can't help you as I live in Yurp.
If your actual goal is not small bottles per se, but safe storage of developer, wine pouches also have (understandably) a low oxygen permeability. Either recycled (may be hard to disconnect the spigot) or bought new (some even have a separate opening for filling. D-76 partly used, one year, no discoloration or loss of activity.
Also, if you are not too far from a university, try contacting the chemistry dept (1-litre brown bottles) or the people in electronics or material science doing photolithography (0.25litre bottles of photoresist; 2.5 litre bottles of isopropanol or acetone, empty of course).