If you want new parts, finding what is available from PM spare parts service (usually called Direct Service or DS) is quite tricky. What I do is:
Find the set on PlaymoDB
3450 - Large CastleFind the part I want e.g.
30 60 0730 - Latch, sliding, for door Enter the part number (without dashes or spaces) at Find Spare Parts (for 7-digit part numbers, add a zero as the eighth digit)
hereIf the part shows as no longer available (as in the example above), go back to the part on PlaymoDB, click on the picture to get the part's page, then click on the link where it says 'Do a Text Search for parts with the same name'
This gives a page with
four similar parts, usually from an identical mould, in several (three in this case) colours. This shows another part number for the black latch, 30617410.
Enter this at Find Spare Parts and,
lo and behold, it's available for 25p!*
If you don't mind used parts, go to eBay, but you will usually pay more than getting new ones from DS.
*The UK website, playmobil.co.uk, gives prices in GBP. Playmobil.de gives them in Euro.