Max Approach slope A320/B737

[PEI_3721]

Bomba, I doubt that a value is published as a limitation.
An aircraft’s capability is a function of the drag margin in the approach configuration, with a power setting sufficient for anti-icing and GA spool-up. An operational assessment normally includes lateral and vertical manoeuvre capability to join and maintain an approach path.

There is normally a division between a straight-in approach and landing - the ability to stabilise and flare on a runway vs an airfield approach.
The requirements for an airfield approach may be not so well defined as for steep approach, and might depend on national or local clearances (also see RNAV GPS approvals). An old example involved the BAe146 operating into Aspen without a precision glidepath, i.e. NPA; this was based on a ~6 deg descent into a valley to provide sufficient distance / time to adjust for lower (3deg?) or a circling approach.
This type of approach is not now recommended as an industry standard, thus I suspect that many authorities will require a precision approach path. However, with something like GPS it might be possible to argue a transition to a lower approach path or circling procedure, but with higher minima.

A steeper approach capability before a ‘circling’ approach might be achieved by flying a higher speed than for a straight-in landing (more drag), but this could require more time / manoeuvring area.
In the types of aircraft being considered I would not expect any approach path greater than 6 deg to be approved – it’s not sensible / economic (approval cost / training / currency).
Approvals are normally easier if based on ‘hard data’, e.g. A318 at LCY and extrapolate to a larger aircraft by demonstration, e.g. 4.5 – 5.5 deg.

If terrain remains a problem consider a specialist curved/segmented procedures based on RNAV waypoints; there are some good examples –
Air New Zealand. Qantas (737) Queenstown
Air Alaska (737) Gastineau
Required navigation performance - Wikipedia, the free encyclopedia
Druk Air into Paro, Bhutan (A318)
The Himalayan airport so dangerous only eight pilots are qualified to land there | Daily Mail Online