1. I've discovered that when a part becomes non-available, then the following factors may be in-play...
1.1 Parts are being replaced at a higher rate than anticipated during routine maintenance due to in-service failures. This implies a poor engineering definition of the service environment, to begin-with. NOTE: in some cases, the service environment may have changed substantially.
1.2 Parts Procurement failed to anticipate production needs and/or the need for spare parts for fleet maintenance.
1.3 Your procurement folks failed to anticipate rising costs and lead-times for special parts procurement.
1.4 Your vendors failed to meet their commitments.
2.1 Chrome plated steel is a fairly high wear capable combination... even though the steel is corrosion prone.
2.2 Passivated A285 is a tough alloy that is highly corrosion resistant... but has galling issues... especially if used at high temperatures with similar alloys.
2.3 KNOWING... not guessing... the circumstances surrounding the use of hardware is essential to finding an adequate substitute. An expensive and specialized coating (such as chrome plate) implies a need for specific service environment protection that cannot be randomly and "lightly" replaced. Substantial justification is essential.
2.4 CAUTION: if Your acft is certificated (FAA) or is built/maintained for/by the DoD, then configuration controls are in-place and material/parts substitutions must be carefully evaluated and approved by the regulating agency. Once an "easy to procure substitute" is in-place for a notoriously hard-to-get part, it is impossible to reverse course when an "aw-shit" is discovered, without an Airworthieness Directive [AD] or a TCTO or STCTO (USAF).
2.5 NOTE: passivated A286 bolt shanks are nominal diameter (no allowance for coating). The fasteners MIGHT be altered by an engineering drawing (creating a new part number) with flash-chrome plating (0.0002 max) or solid film lubricant. This option usually presents it's own challenges and headaches...
Regards, Wil Taylor