The most easily aviable brands are HW, Siku and Majorette – most of the time you get what you want with some pation and travel around a bit. MBX is more difficult, as not many shops carry MBX, we tend to miss some batches, the same for 5-Packs.
For Siku the prices may differ from store to store : for a current Audi Q5 you may pay everything beween 4.90 up to 7.90 ! Cheapest is Migros. For HW, MJ and MBX the prices only differ for less than a buck. If they carry HW most of the time they also have 5-Packs.
The following list is out of my experience and can locally differ especially for the size of the shops.

MIGROS (supermarket, departement store) : HW, HW Mystery, HW medium (currently Batman, Rally), HW Premium, Majorette (several lines), MBX (up to 2019 Batch C/D), MBX 5-Pack (2019), Maisto medium

MÜLLER (drugstore/toyshop): HW, HW medium (old stock), HW 5-Pack, HW Premium, MBX (2018), MBX 5-Pack, Siku, Maisto Fresh Metal, Bburago Ferrari

COOP (supermarket, departement store): HW (overpriced), HW 5-Pack, Siku, MBX 5-Pack, Majorette (several lines, only Coop City), Maisto Harley Davidson (Coop City), Bburago Ferrari, MBX (only Superstores), MJ 3-Pack 2014 (Coop City/Superstores) – this chain is ushally far behind the scedule

MANOR (departement store): HW, Majorette, Maisto Fresh Metal, Siku, Bburago Ferrari

GLOBUS (departement store): HW, HW Premium, MBX, Siku, Bburago {if you have two shops in the same town only the one farer in the mall has toys} – currently owned by Migros

FRANZ CARL WEBER (toy shop): HW, HW medium, HW Premium (tend to disapear quick), HW 10-Pack, HW 5-Pack, HW 3-Pack, Siku, Maisto friction, Bburago Ferrari, Schuco (only in bigger shops)

OTTOS (surplus/discounter): HW Mystery, HW 5-Pack, MBX 5-Pack, Maisto friction, Bburago, sometimes other lesser known brands

SMYTHS former TRU (toy shop): HW, Siku, Majorette

SPIELKISTE (toy shop): Siku, Majorette (some lines), HW

LANDI (hardware/departement store) : Majorette (some lines) - {recently they kicked out Siku}

MAXI TOYS (toy shop): HW, HW Premium, Siku

KING JOUET (toy shop): HW, HW Premium, HW 5-Pack, HW3-Pack, HW 10-Pack, Siku, Bburago Ferrari - {recently they kicked out Majorette}

LOEB, Bern, Biel (departement store): HW, Siku, MBX 5-Pack

SCHELLENBERGER, Thun (departement store): Siku, HW, Maisto friction, Maisto Harley, Bburago Ferrari, MB 5-Pack

ALDI/LIDL (discounter): ushally nothing but up a wile show up Welly 20/30-Pack or HW 5-Pack

JUMBO (hardware store): Maisto Fresh Metal

Local toy shops: Most have Siku and HW, other brands may pop up too

Trift shops/second hand: Brocki (Heilsarmee/Armée du salut), HIOB, Emmaus, la Trouvaille (Red Cross), Brockenstube (Frauenverein) – with some luck you find some things for a good price.
If there is a flea market (Flohmarkt, Flohmärit, Brocante, Antiquitätenmesse, Sammlermesse) in the town your are visiting it is worth a visit – also only to look. Source: http://www.flohmarkttermine.ch.