The handle and latch/lock are sold separately but both are still available direct from Bosch. This model was sold in the UK and Australia, but I'll assume for the moment you are in the UK and provide details for for ordering parts in the UK.
Plastic handle for Bosch SMS4012
Bosch part number: 056219
Lock for Bosch SMS4012
Bosch part number: 056218
Both parts are in stock and ready to ship. Bosch have a standard delivery charge of £5 per order.
You probably only need to order one of the above parts. You said it wont open/close, so you probably only need the lock unless the plastic handle is cracked/broken as well.
With regard to replacing it yourself, it's fiddly and requires some dis-assembly of the door and control panel but it can be done on a DIY basis if you're patient, practical and you know the difference between a pair of pliers and a screwdriver ;) (you'll need both)
It's not the most difficult job on the washer but it's not the easiest either so you may want to consider calling a professional. You could also order the parts yourself and pay someone to fit them as this usually saves a bit of money, but you should inform them beforehand that you will be doing so. Some engineers make extra profit on the parts and aren't keen on having the parts supplied!
Either way, the parts are still available so the dishwasher can be repaired. If you are not in the UK please let me know, but the part numbers should be the same wherever you are.
If you decide you want to try replacing it yourself, I can provide further guidance, but this washer was made before I started repairing dishwashers and I don't see many of these washers now. It's one of those repairs I could do if I had the machine in front of me but providing step by step instructions without being able to see it is a little more difficult - but not impossible! You will probably have to figure out one or two bits for yourself . . .
Hope this helps. Please let me know if you would like further assistance.