There's
Farnell :
https://uk.farnell.com/c/transformers - filter further by Isolation Transformers and Toroidal Power Transformers
Note that there's an "official distributor" for Croatia : Altpro D.O.O - see
https://export.farnell.com/export-portal or just try
https://export.farnell.com/RS Components - they have a Croatia sub-site:
https://hr.rsdelivers.com/See
https://uk.rs-online.com/web/c/power-supplies-transformers/transformers/ - filter further by PCB transformers , chassis, toroidal ...
TME.eu - good Polish company, should ship to Croatia :
https://www.tme.eu/en/katalog/transformers-and-ferrite-cores_100440/Also, should be more clear about exactly what you need.
Do you need 24v AC or 24v DC (after rectification using a bridge rectifier, linear regulator etc) ?
Transformers have a VA rating ...
IF you need 24v AC , like for example to light a 75w incandescent lightbulb, then you could go for a 75VA transformer.
if you want to convert output to DC by using a bridge rectifier, then you can approximate the DC voltage and DC current with the formulas:
Vdc peak = sqrt(2) x Vac - 2 x Vdiode = ~ 1.414 x Vac - 1.5v
Current DC = ~ 0.62 x Current AC
Capacitance required = Current / 2 x AC frequency x [V dc peak - Vdc min]
So for example, if you have a 24v AC transformer with a 100VA rating ( 100VA / 24v = 4.16A) then you'll get a DC voltage with a peak close to 1.414 x 24 - 1.5 = 32v peak and current would be ~ 0.62x4.16 = ~ 2.6A
You'd need C = 2.6 / 2 x 60Hz x (32v - 24v) = 2.6/960 = 0.002708 Farads or ~ 2700uF 50v minimum to keep the DC voltage above 24v at all times.
So if you want a voltage up to 32V DC (depending on how big your smoothing capacitor would be) and up to 3A, you'll need more than 100VA...