Two things I did that helped me get access and later-on keep the door open to my grief. Sometimes I still do no. 2, no. 1 I don't need anymore.
1. Suggested to me by therapists in a hospital:
Choose a spot in your home that where you feel good (just normal, not especially safe or anything), for example a corner in the bed-room). Choose a chair (it should be something moveable, so not really the sofa) that feels okay for the purpose. Choose a day and time span when you invest into your grieving, say: Saturday, starting at 12:30, ending at 13:00 (not longer than 30 minutes; I did 15 and that was more than enough). At that very day and time, each week, no exceptions (plan around it and by doing so accreddit it its meaningfulness (sorry if my English is lacking)) take the chair and put it in the corner, sit down on it and just think of why you're sitting on the chair. Let the thoughts and feelings come. If nothing happens for the 15 minutes, nothing happens for the 15 minutes. Still spend the time on the chair. If you break down after two minutes and can not seem to stop at the end you set for yourself (e.g. at 12:45), leave the chair at precisely 12:45 no matter if you're still crying or not. Put the chair back to where it usually is and go sit somewhere else, preferably not in the same room.
This may seem (it did to me) "artificial", a bit like acting maybe, in the beginning. It helps though. Sooner or later, that was my time and place for grief. The set ending time is vital! If you decide to try this, I'd suggest (out of experience) to try it at least 4-8 times before stopping again for good. It really feels awkward at first, also when there seem to be no feelings in you at all as soon as on that chair.
2. Using objects and rituals:
For example, if you want to grieve about someone who has died recently (for example), make a little boat from paper, taking time while making it to let the thoughts and feelings come (memories, hopes, dreams, etc.). Then take that little boat to a nearby river or lake, etc., choose a spot you feel is good for you and make the person's leaving visible to you by putting the boat in the water and letting it sail away. Stay there, watch it and feel. Once the boat is gone, either being carried away by little waves or even drowning because of the paper getting wet, feel what that does to you.
There are a lot of things that you can do or use for making "visible analogies". Those have helped me realise that e.g. the person died and that I was left behind being sad and desperate and whatever else. In the end, by using such rituals I gave the goodbye space and meaningfulness. Our lives are so fast-paces, I need to take time-outs like this to process e.g. deaths, people leaving, etc. It is always good to set a day and beginning and ending time. The ending time being vital, really.
Maybe this helps. If not, keep looking for the ones that may help you. I am sure they're out there.