What you need is a E27 60w traffic signal lamp unigirl. These lamps are commonly used in roadside traffic signalling equipment and pedestrian walkways in the USA and UK. The base looks like the solder blob has been filed flat as you describe. Don't play about with adding a solder blob to the tab and I wouldn't consider the problem drastic enough to buy a new security lamp fitting. These lamps are readily available from electrical wholesalers throughout the UK and right now, are some of the few incandescent lamps that can continue to be sold after the banning of incandescent lamps by the EU. I'm surprised that an electrician seemed unaware of this lamp type.